Add m-esr52 at 52.6.0

1 files changed, 2371 insertions, 0 deletions

diff --git a/xpcom/glue/nsTArray.h b/xpcom/glue/nsTArray.h
new file mode 100644
index 000000000..ca74a41f7
--- /dev/null
+++ b/xpcom/glue/nsTArray.h
@@ -0,0 +1,2371 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsTArray_h__
+#define nsTArray_h__
+
+#include "nsTArrayForwardDeclare.h"
+#include "mozilla/Alignment.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/BinarySearch.h"
+#include "mozilla/fallible.h"
+#include "mozilla/Function.h"
+#include "mozilla/MathAlgorithms.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/Move.h"
+#include "mozilla/ReverseIterator.h"
+#include "mozilla/TypeTraits.h"
+
+#include <string.h>
+
+#include "nsCycleCollectionNoteChild.h"
+#include "nsAlgorithm.h"
+#include "nscore.h"
+#include "nsQuickSort.h"
+#include "nsDebug.h"
+#include "nsISupportsImpl.h"
+#include "nsRegionFwd.h"
+#include <initializer_list>
+#include <new>
+
+namespace JS {
+template<class T>
+class Heap;
+class ObjectPtr;
+} /* namespace JS */
+
+class nsRegion;
+namespace mozilla {
+namespace layers {
+struct TileClient;
+} // namespace layers
+} // namespace mozilla
+
+namespace mozilla {
+struct SerializedStructuredCloneBuffer;
+} // namespace mozilla
+
+namespace mozilla {
+namespace dom {
+namespace ipc {
+class StructuredCloneData;
+} // namespace ipc
+} // namespace dom
+} // namespace mozilla
+
+namespace mozilla {
+namespace dom {
+class ClonedMessageData;
+class MessagePortMessage;
+namespace indexedDB {
+struct StructuredCloneReadInfo;
+class SerializedStructuredCloneReadInfo;
+class ObjectStoreCursorResponse;
+} // namespace indexedDB
+} // namespace dom
+} // namespace mozilla
+
+class JSStructuredCloneData;
+
+//
+// nsTArray is a resizable array class, like std::vector.
+//
+// Unlike std::vector, which follows C++'s construction/destruction rules,
+// nsTArray assumes that your "T" can be memmoved()'ed safely.
+//
+// The public classes defined in this header are
+//
+//   nsTArray<T>,
+//   FallibleTArray<T>,
+//   AutoTArray<T, N>, and
+//
+// nsTArray and AutoTArray are infallible by default. To opt-in to fallible
+// behaviour, use the `mozilla::fallible` parameter and check the return value.
+//
+// If you just want to declare the nsTArray types (e.g., if you're in a header
+// file and don't need the full nsTArray definitions) consider including
+// nsTArrayForwardDeclare.h instead of nsTArray.h.
+//
+// The template parameter (i.e., T in nsTArray<T>) specifies the type of the
+// elements and has the following requirements:
+//
+//   T MUST be safely memmove()'able.
+//   T MUST define a copy-constructor.
+//   T MAY define operator< for sorting.
+//   T MAY define operator== for searching.
+//
+// (Note that the memmove requirement may be relaxed for certain types - see
+// nsTArray_CopyChooser below.)
+//
+// For methods taking a Comparator instance, the Comparator must be a class
+// defining the following methods:
+//
+//   class Comparator {
+//     public:
+//       /** @return True if the elements are equals; false otherwise. */
+//       bool Equals(const elem_type& a, const Item& b) const;
+//
+//       /** @return True if (a < b); false otherwise. */
+//       bool LessThan(const elem_type& a, const Item& b) const;
+//   };
+//
+// The Equals method is used for searching, and the LessThan method is used for
+// searching and sorting.  The |Item| type above can be arbitrary, but must
+// match the Item type passed to the sort or search function.
+//
+
+
+//
+// nsTArrayFallibleResult and nsTArrayInfallibleResult types are proxy types
+// which are used because you cannot use a templated type which is bound to
+// void as an argument to a void function.  In order to work around that, we
+// encode either a void or a boolean inside these proxy objects, and pass them
+// to the aforementioned function instead, and then use the type information to
+// decide what to do in the function.
+//
+// Note that public nsTArray methods should never return a proxy type.  Such
+// types are only meant to be used in the internal nsTArray helper methods.
+// Public methods returning non-proxy types cannot be called from other
+// nsTArray members.
+//
+struct nsTArrayFallibleResult
+{
+  // Note: allows implicit conversions from and to bool
+  MOZ_IMPLICIT nsTArrayFallibleResult(bool aResult) : mResult(aResult) {}
+
+  MOZ_IMPLICIT operator bool() { return mResult; }
+
+private:
+  bool mResult;
+};
+
+struct nsTArrayInfallibleResult
+{
+};
+
+//
+// nsTArray*Allocators must all use the same |free()|, to allow swap()'ing
+// between fallible and infallible variants.
+//
+
+struct nsTArrayFallibleAllocatorBase
+{
+  typedef bool ResultType;
+  typedef nsTArrayFallibleResult ResultTypeProxy;
+
+  static ResultType Result(ResultTypeProxy aResult) { return aResult; }
+  static bool Successful(ResultTypeProxy aResult) { return aResult; }
+  static ResultTypeProxy SuccessResult() { return true; }
+  static ResultTypeProxy FailureResult() { return false; }
+  static ResultType ConvertBoolToResultType(bool aValue) { return aValue; }
+};
+
+struct nsTArrayInfallibleAllocatorBase
+{
+  typedef void ResultType;
+  typedef nsTArrayInfallibleResult ResultTypeProxy;
+
+  static ResultType Result(ResultTypeProxy aResult) {}
+  static bool Successful(ResultTypeProxy) { return true; }
+  static ResultTypeProxy SuccessResult() { return ResultTypeProxy(); }
+
+  static ResultTypeProxy FailureResult()
+  {
+    NS_RUNTIMEABORT("Infallible nsTArray should never fail");
+    return ResultTypeProxy();
+  }
+
+  static ResultType ConvertBoolToResultType(bool aValue)
+  {
+    if (!aValue) {
+      NS_RUNTIMEABORT("infallible nsTArray should never convert false to ResultType");
+    }
+  }
+};
+
+struct nsTArrayFallibleAllocator : nsTArrayFallibleAllocatorBase
+{
+  static void* Malloc(size_t aSize) { return malloc(aSize); }
+  static void* Realloc(void* aPtr, size_t aSize)
+  {
+    return realloc(aPtr, aSize);
+  }
+
+  static void Free(void* aPtr) { free(aPtr); }
+  static void SizeTooBig(size_t) {}
+};
+
+#if defined(MOZALLOC_HAVE_XMALLOC)
+#include "mozilla/mozalloc_abort.h"
+
+struct nsTArrayInfallibleAllocator : nsTArrayInfallibleAllocatorBase
+{
+  static void* Malloc(size_t aSize) { return moz_xmalloc(aSize); }
+  static void* Realloc(void* aPtr, size_t aSize)
+  {
+    return moz_xrealloc(aPtr, aSize);
+  }
+
+  static void Free(void* aPtr) { free(aPtr); }
+  static void SizeTooBig(size_t aSize) { NS_ABORT_OOM(aSize); }
+};
+
+#else
+#include <stdlib.h>
+
+struct nsTArrayInfallibleAllocator : nsTArrayInfallibleAllocatorBase
+{
+  static void* Malloc(size_t aSize)
+  {
+    void* ptr = malloc(aSize);
+    if (MOZ_UNLIKELY(!ptr)) {
+      NS_ABORT_OOM(aSize);
+    }
+    return ptr;
+  }
+
+  static void* Realloc(void* aPtr, size_t aSize)
+  {
+    void* newptr = realloc(aPtr, aSize);
+    if (MOZ_UNLIKELY(!newptr && aSize)) {
+      NS_ABORT_OOM(aSize);
+    }
+    return newptr;
+  }
+
+  static void Free(void* aPtr) { free(aPtr); }
+  static void SizeTooBig(size_t aSize) { NS_ABORT_OOM(aSize); }
+};
+
+#endif
+
+// nsTArray_base stores elements into the space allocated beyond
+// sizeof(*this).  This is done to minimize the size of the nsTArray
+// object when it is empty.
+struct nsTArrayHeader
+{
+  static nsTArrayHeader sEmptyHdr;
+
+  uint32_t mLength;
+  uint32_t mCapacity : 31;
+  uint32_t mIsAutoArray : 1;
+};
+
+// This class provides a SafeElementAt method to nsTArray<T*> which does
+// not take a second default value parameter.
+template<class E, class Derived>
+struct nsTArray_SafeElementAtHelper
+{
+  typedef E*       elem_type;
+  typedef size_t   index_type;
+
+  // No implementation is provided for these two methods, and that is on
+  // purpose, since we don't support these functions on non-pointer type
+  // instantiations.
+  elem_type& SafeElementAt(index_type aIndex);
+  const elem_type& SafeElementAt(index_type aIndex) const;
+};
+
+template<class E, class Derived>
+struct nsTArray_SafeElementAtHelper<E*, Derived>
+{
+  typedef E*       elem_type;
+  //typedef const E* const_elem_type;   XXX: see below
+  typedef size_t   index_type;
+
+  elem_type SafeElementAt(index_type aIndex)
+  {
+    return static_cast<Derived*>(this)->SafeElementAt(aIndex, nullptr);
+  }
+
+  // XXX: Probably should return const_elem_type, but callsites must be fixed.
+  // Also, the use of const_elem_type for nsTArray<xpcGCCallback> in
+  // xpcprivate.h causes build failures on Windows because xpcGCCallback is a
+  // function pointer and MSVC doesn't like qualifying it with |const|.
+  elem_type SafeElementAt(index_type aIndex) const
+  {
+    return static_cast<const Derived*>(this)->SafeElementAt(aIndex, nullptr);
+  }
+};
+
+// E is the base type that the smart pointer is templated over; the
+// smart pointer can act as E*.
+template<class E, class Derived>
+struct nsTArray_SafeElementAtSmartPtrHelper
+{
+  typedef E*       elem_type;
+  typedef const E* const_elem_type;
+  typedef size_t   index_type;
+
+  elem_type SafeElementAt(index_type aIndex)
+  {
+    return static_cast<Derived*>(this)->SafeElementAt(aIndex, nullptr);
+  }
+
+  // XXX: Probably should return const_elem_type, but callsites must be fixed.
+  elem_type SafeElementAt(index_type aIndex) const
+  {
+    return static_cast<const Derived*>(this)->SafeElementAt(aIndex, nullptr);
+  }
+};
+
+template<class T> class nsCOMPtr;
+
+template<class E, class Derived>
+struct nsTArray_SafeElementAtHelper<nsCOMPtr<E>, Derived>
+  : public nsTArray_SafeElementAtSmartPtrHelper<E, Derived>
+{
+};
+
+template<class E, class Derived>
+struct nsTArray_SafeElementAtHelper<RefPtr<E>, Derived>
+  : public nsTArray_SafeElementAtSmartPtrHelper<E, Derived>
+{
+};
+
+namespace mozilla {
+template<class T> class OwningNonNull;
+} // namespace mozilla
+
+template<class E, class Derived>
+struct nsTArray_SafeElementAtHelper<mozilla::OwningNonNull<E>, Derived>
+{
+  typedef E*       elem_type;
+  typedef const E* const_elem_type;
+  typedef size_t   index_type;
+
+  elem_type SafeElementAt(index_type aIndex)
+  {
+    if (aIndex < static_cast<Derived*>(this)->Length()) {
+      return static_cast<Derived*>(this)->ElementAt(aIndex);
+    }
+    return nullptr;
+  }
+
+  // XXX: Probably should return const_elem_type, but callsites must be fixed.
+  elem_type SafeElementAt(index_type aIndex) const
+  {
+    if (aIndex < static_cast<const Derived*>(this)->Length()) {
+      return static_cast<const Derived*>(this)->ElementAt(aIndex);
+    }
+    return nullptr;
+  }
+};
+
+// Servo bindings.
+extern "C" void Gecko_EnsureTArrayCapacity(void* aArray,
+                                           size_t aCapacity,
+                                           size_t aElementSize);
+extern "C" void Gecko_ClearPODTArray(void* aArray,
+                                     size_t aElementSize,
+                                     size_t aElementAlign);
+
+MOZ_NORETURN MOZ_COLD void
+InvalidArrayIndex_CRASH(size_t aIndex, size_t aLength);
+
+//
+// This class serves as a base class for nsTArray.  It shouldn't be used
+// directly.  It holds common implementation code that does not depend on the
+// element type of the nsTArray.
+//
+template<class Alloc, class Copy>
+class nsTArray_base
+{
+  // Allow swapping elements with |nsTArray_base|s created using a
+  // different allocator.  This is kosher because all allocators use
+  // the same free().
+  template<class Allocator, class Copier>
+  friend class nsTArray_base;
+  friend void Gecko_EnsureTArrayCapacity(void* aArray, size_t aCapacity,
+                                         size_t aElemSize);
+  friend void Gecko_ClearPODTArray(void* aTArray, size_t aElementSize,
+                                   size_t aElementAlign);
+
+protected:
+  typedef nsTArrayHeader Header;
+
+public:
+  typedef size_t size_type;
+  typedef size_t index_type;
+
+  // @return The number of elements in the array.
+  size_type Length() const { return mHdr->mLength; }
+
+  // @return True if the array is empty or false otherwise.
+  bool IsEmpty() const { return Length() == 0; }
+
+  // @return The number of elements that can fit in the array without forcing
+  // the array to be re-allocated.  The length of an array is always less
+  // than or equal to its capacity.
+  size_type Capacity() const {  return mHdr->mCapacity; }
+
+#ifdef DEBUG
+  void* DebugGetHeader() const { return mHdr; }
+#endif
+
+protected:
+  nsTArray_base();
+
+  ~nsTArray_base();
+
+  // Resize the storage if necessary to achieve the requested capacity.
+  // @param aCapacity The requested number of array elements.
+  // @param aElemSize The size of an array element.
+  // @return False if insufficient memory is available; true otherwise.
+  template<typename ActualAlloc>
+  typename ActualAlloc::ResultTypeProxy EnsureCapacity(size_type aCapacity,
+                                                       size_type aElemSize);
+
+  // Tries to resize the storage to the minimum required amount. If this fails,
+  // the array is left as-is.
+  // @param aElemSize  The size of an array element.
+  // @param aElemAlign The alignment in bytes of an array element.
+  void ShrinkCapacity(size_type aElemSize, size_t aElemAlign);
+
+  // This method may be called to resize a "gap" in the array by shifting
+  // elements around.  It updates mLength appropriately.  If the resulting
+  // array has zero elements, then the array's memory is free'd.
+  // @param aStart     The starting index of the gap.
+  // @param aOldLen    The current length of the gap.
+  // @param aNewLen    The desired length of the gap.
+  // @param aElemSize  The size of an array element.
+  // @param aElemAlign The alignment in bytes of an array element.
+  template<typename ActualAlloc>
+  void ShiftData(index_type aStart, size_type aOldLen, size_type aNewLen,
+                 size_type aElemSize, size_t aElemAlign);
+
+  // This method increments the length member of the array's header.
+  // Note that mHdr may actually be sEmptyHdr in the case where a
+  // zero-length array is inserted into our array. But then aNum should
+  // always be 0.
+  void IncrementLength(size_t aNum)
+  {
+    if (mHdr == EmptyHdr()) {
+      if (MOZ_UNLIKELY(aNum != 0)) {
+        // Writing a non-zero length to the empty header would be extremely bad.
+        MOZ_CRASH();
+      }
+    } else {
+      mHdr->mLength += aNum;
+    }
+  }
+
+  // This method inserts blank slots into the array.
+  // @param aIndex the place to insert the new elements. This must be no
+  //               greater than the current length of the array.
+  // @param aCount the number of slots to insert
+  // @param aElementSize the size of an array element.
+  // @param aElemAlign the alignment in bytes of an array element.
+  template<typename ActualAlloc>
+  bool InsertSlotsAt(index_type aIndex, size_type aCount,
+                     size_type aElementSize, size_t aElemAlign);
+
+  template<typename ActualAlloc, class Allocator>
+  typename ActualAlloc::ResultTypeProxy
+  SwapArrayElements(nsTArray_base<Allocator, Copy>& aOther,
+                    size_type aElemSize,
+                    size_t aElemAlign);
+
+  // This is an RAII class used in SwapArrayElements.
+  class IsAutoArrayRestorer
+  {
+  public:
+    IsAutoArrayRestorer(nsTArray_base<Alloc, Copy>& aArray, size_t aElemAlign);
+    ~IsAutoArrayRestorer();
+
+  private:
+    nsTArray_base<Alloc, Copy>& mArray;
+    size_t mElemAlign;
+    bool mIsAuto;
+  };
+
+  // Helper function for SwapArrayElements. Ensures that if the array
+  // is an AutoTArray that it doesn't use the built-in buffer.
+  template<typename ActualAlloc>
+  bool EnsureNotUsingAutoArrayBuffer(size_type aElemSize);
+
+  // Returns true if this nsTArray is an AutoTArray with a built-in buffer.
+  bool IsAutoArray() const { return mHdr->mIsAutoArray; }
+
+  // Returns a Header for the built-in buffer of this AutoTArray.
+  Header* GetAutoArrayBuffer(size_t aElemAlign)
+  {
+    MOZ_ASSERT(IsAutoArray(), "Should be an auto array to call this");
+    return GetAutoArrayBufferUnsafe(aElemAlign);
+  }
+  const Header* GetAutoArrayBuffer(size_t aElemAlign) const
+  {
+    MOZ_ASSERT(IsAutoArray(), "Should be an auto array to call this");
+    return GetAutoArrayBufferUnsafe(aElemAlign);
+  }
+
+  // Returns a Header for the built-in buffer of this AutoTArray, but doesn't
+  // assert that we are an AutoTArray.
+  Header* GetAutoArrayBufferUnsafe(size_t aElemAlign)
+  {
+    return const_cast<Header*>(static_cast<const nsTArray_base<Alloc, Copy>*>(
+      this)->GetAutoArrayBufferUnsafe(aElemAlign));
+  }
+  const Header* GetAutoArrayBufferUnsafe(size_t aElemAlign) const;
+
+  // Returns true if this is an AutoTArray and it currently uses the
+  // built-in buffer to store its elements.
+  bool UsesAutoArrayBuffer() const;
+
+  // The array's elements (prefixed with a Header).  This pointer is never
+  // null.  If the array is empty, then this will point to sEmptyHdr.
+  Header* mHdr;
+
+  Header* Hdr() const { return mHdr; }
+  Header** PtrToHdr() { return &mHdr; }
+  static Header* EmptyHdr() { return &Header::sEmptyHdr; }
+};
+
+//
+// This class defines convenience functions for element specific operations.
+// Specialize this template if necessary.
+//
+template<class E>
+class nsTArrayElementTraits
+{
+public:
+  // Invoke the default constructor in place.
+  static inline void Construct(E* aE)
+  {
+    // Do NOT call "E()"! That triggers C++ "default initialization"
+    // which zeroes out POD ("plain old data") types such as regular
+    // ints.  We don't want that because it can be a performance issue
+    // and people don't expect it; nsTArray should work like a regular
+    // C/C++ array in this respect.
+    new (static_cast<void*>(aE)) E;
+  }
+  // Invoke the copy-constructor in place.
+  template<class A>
+  static inline void Construct(E* aE, A&& aArg)
+  {
+    typedef typename mozilla::RemoveCV<E>::Type E_NoCV;
+    typedef typename mozilla::RemoveCV<A>::Type A_NoCV;
+    static_assert(!mozilla::IsSame<E_NoCV*, A_NoCV>::value,
+                  "For safety, we disallow constructing nsTArray<E> elements "
+                  "from E* pointers. See bug 960591.");
+    new (static_cast<void*>(aE)) E(mozilla::Forward<A>(aArg));
+  }
+  // Invoke the destructor in place.
+  static inline void Destruct(E* aE) { aE->~E(); }
+};
+
+// The default comparator used by nsTArray
+template<class A, class B>
+class nsDefaultComparator
+{
+public:
+  bool Equals(const A& aA, const B& aB) const { return aA == aB; }
+  bool LessThan(const A& aA, const B& aB) const { return aA < aB; }
+};
+
+template<bool IsPod, bool IsSameType>
+struct AssignRangeAlgorithm
+{
+  template<class Item, class ElemType, class IndexType, class SizeType>
+  static void implementation(ElemType* aElements, IndexType aStart,
+                             SizeType aCount, const Item* aValues)
+  {
+    ElemType* iter = aElements + aStart;
+    ElemType* end = iter + aCount;
+    for (; iter != end; ++iter, ++aValues) {
+      nsTArrayElementTraits<ElemType>::Construct(iter, *aValues);
+    }
+  }
+};
+
+template<>
+struct AssignRangeAlgorithm<true, true>
+{
+  template<class Item, class ElemType, class IndexType, class SizeType>
+  static void implementation(ElemType* aElements, IndexType aStart,
+                             SizeType aCount, const Item* aValues)
+  {
+    memcpy(aElements + aStart, aValues, aCount * sizeof(ElemType));
+  }
+};
+
+//
+// Normally elements are copied with memcpy and memmove, but for some element
+// types that is problematic.  The nsTArray_CopyChooser template class can be
+// specialized to ensure that copying calls constructors and destructors
+// instead, as is done below for JS::Heap<E> elements.
+//
+
+//
+// A class that defines how to copy elements using memcpy/memmove.
+//
+struct nsTArray_CopyWithMemutils
+{
+  const static bool allowRealloc = true;
+
+  static void MoveNonOverlappingRegionWithHeader(void* aDest, const void* aSrc,
+                                                 size_t aCount, size_t aElemSize)
+  {
+    memcpy(aDest, aSrc, sizeof(nsTArrayHeader) + aCount * aElemSize);
+  }
+
+  static void MoveOverlappingRegion(void* aDest, void* aSrc, size_t aCount,
+                                    size_t aElemSize)
+  {
+    memmove(aDest, aSrc, aCount * aElemSize);
+  }
+
+  static void MoveNonOverlappingRegion(void* aDest, void* aSrc, size_t aCount,
+                                       size_t aElemSize)
+  {
+    memcpy(aDest, aSrc, aCount * aElemSize);
+  }
+};
+
+//
+// A template class that defines how to copy elements calling their constructors
+// and destructors appropriately.
+//
+template<class ElemType>
+struct nsTArray_CopyWithConstructors
+{
+  typedef nsTArrayElementTraits<ElemType> traits;
+
+  const static bool allowRealloc = false;
+
+  static void MoveNonOverlappingRegionWithHeader(void* aDest, void* aSrc, size_t aCount,
+                                                 size_t aElemSize)
+  {
+    nsTArrayHeader* destHeader = static_cast<nsTArrayHeader*>(aDest);
+    nsTArrayHeader* srcHeader = static_cast<nsTArrayHeader*>(aSrc);
+    *destHeader = *srcHeader;
+    MoveNonOverlappingRegion(static_cast<uint8_t*>(aDest) + sizeof(nsTArrayHeader),
+                             static_cast<uint8_t*>(aSrc) + sizeof(nsTArrayHeader),
+                             aCount, aElemSize);
+  }
+
+  // These functions are defined by analogy with memmove and memcpy.
+  // What they actually do is slightly different: MoveOverlappingRegion
+  // checks to see which direction the movement needs to take place,
+  // whether from back-to-front of the range to be moved or from
+  // front-to-back.  MoveNonOverlappingRegion assumes that moving
+  // front-to-back is always valid.  So they're really more like
+  // std::move{_backward,} in that respect.  We keep these names because
+  // we think they read slightly better, and MoveNonOverlappingRegion is
+  // only ever called on overlapping regions from MoveOverlappingRegion.
+  static void MoveOverlappingRegion(void* aDest, void* aSrc, size_t aCount,
+                                    size_t aElemSize)
+  {
+    ElemType* destElem = static_cast<ElemType*>(aDest);
+    ElemType* srcElem = static_cast<ElemType*>(aSrc);
+    ElemType* destElemEnd = destElem + aCount;
+    ElemType* srcElemEnd = srcElem + aCount;
+    if (destElem == srcElem) {
+      return;  // In practice, we don't do this.
+    }
+
+    // Figure out whether to copy back-to-front or front-to-back.
+    if (srcElemEnd > destElem && srcElemEnd < destElemEnd) {
+      while (destElemEnd != destElem) {
+        --destElemEnd;
+        --srcElemEnd;
+        traits::Construct(destElemEnd, mozilla::Move(*srcElemEnd));
+        traits::Destruct(srcElemEnd);
+      }
+    } else {
+      MoveNonOverlappingRegion(aDest, aSrc, aCount, aElemSize);
+    }
+  }
+
+  static void MoveNonOverlappingRegion(void* aDest, void* aSrc, size_t aCount,
+                                       size_t aElemSize)
+  {
+    ElemType* destElem = static_cast<ElemType*>(aDest);
+    ElemType* srcElem = static_cast<ElemType*>(aSrc);
+    ElemType* destElemEnd = destElem + aCount;
+#ifdef DEBUG
+    ElemType* srcElemEnd = srcElem + aCount;
+    MOZ_ASSERT(srcElemEnd <= destElem || srcElemEnd > destElemEnd);
+#endif
+    while (destElem != destElemEnd) {
+      traits::Construct(destElem, mozilla::Move(*srcElem));
+      traits::Destruct(srcElem);
+      ++destElem;
+      ++srcElem;
+    }
+  }
+};
+
+//
+// The default behaviour is to use memcpy/memmove for everything.
+//
+template<class E>
+struct MOZ_NEEDS_MEMMOVABLE_TYPE nsTArray_CopyChooser
+{
+  using Type = nsTArray_CopyWithMemutils;
+};
+
+//
+// Some classes require constructors/destructors to be called, so they are
+// specialized here.
+//
+#define DECLARE_USE_COPY_CONSTRUCTORS(T)                \
+  template<>                                            \
+  struct nsTArray_CopyChooser<T>                        \
+  {                                                     \
+    using Type = nsTArray_CopyWithConstructors<T>;      \
+  };
+
+#define DECLARE_USE_COPY_CONSTRUCTORS_FOR_TEMPLATE(T)   \
+  template<typename S>                                  \
+  struct nsTArray_CopyChooser<T<S>>                     \
+  {                                                     \
+    using Type = nsTArray_CopyWithConstructors<T<S>>;   \
+  };
+
+DECLARE_USE_COPY_CONSTRUCTORS_FOR_TEMPLATE(JS::Heap)
+
+DECLARE_USE_COPY_CONSTRUCTORS(nsRegion)
+DECLARE_USE_COPY_CONSTRUCTORS(nsIntRegion)
+DECLARE_USE_COPY_CONSTRUCTORS(mozilla::layers::TileClient)
+DECLARE_USE_COPY_CONSTRUCTORS(mozilla::SerializedStructuredCloneBuffer)
+DECLARE_USE_COPY_CONSTRUCTORS(mozilla::dom::ipc::StructuredCloneData)
+DECLARE_USE_COPY_CONSTRUCTORS(mozilla::dom::ClonedMessageData)
+DECLARE_USE_COPY_CONSTRUCTORS(mozilla::dom::indexedDB::StructuredCloneReadInfo);
+DECLARE_USE_COPY_CONSTRUCTORS(mozilla::dom::indexedDB::ObjectStoreCursorResponse)
+DECLARE_USE_COPY_CONSTRUCTORS(mozilla::dom::indexedDB::SerializedStructuredCloneReadInfo);
+DECLARE_USE_COPY_CONSTRUCTORS(JSStructuredCloneData)
+DECLARE_USE_COPY_CONSTRUCTORS(mozilla::dom::MessagePortMessage)
+DECLARE_USE_COPY_CONSTRUCTORS(JS::ObjectPtr)
+
+
+//
+// Base class for nsTArray_Impl that is templated on element type and derived
+// nsTArray_Impl class, to allow extra conversions to be added for specific
+// types.
+//
+template<class E, class Derived>
+struct nsTArray_TypedBase : public nsTArray_SafeElementAtHelper<E, Derived>
+{
+};
+
+//
+// Specialization of nsTArray_TypedBase for arrays containing JS::Heap<E>
+// elements.
+//
+// These conversions are safe because JS::Heap<E> and E share the same
+// representation, and since the result of the conversions are const references
+// we won't miss any barriers.
+//
+// The static_cast is necessary to obtain the correct address for the derived
+// class since we are a base class used in multiple inheritance.
+//
+template<class E, class Derived>
+struct nsTArray_TypedBase<JS::Heap<E>, Derived>
+  : public nsTArray_SafeElementAtHelper<JS::Heap<E>, Derived>
+{
+  operator const nsTArray<E>&()
+  {
+    static_assert(sizeof(E) == sizeof(JS::Heap<E>),
+                  "JS::Heap<E> must be binary compatible with E.");
+    Derived* self = static_cast<Derived*>(this);
+    return *reinterpret_cast<nsTArray<E> *>(self);
+  }
+
+  operator const FallibleTArray<E>&()
+  {
+    Derived* self = static_cast<Derived*>(this);
+    return *reinterpret_cast<FallibleTArray<E> *>(self);
+  }
+};
+
+namespace detail {
+
+template<class Item, class Comparator>
+struct ItemComparatorEq
+{
+  const Item& mItem;
+  const Comparator& mComp;
+  ItemComparatorEq(const Item& aItem, const Comparator& aComp)
+    : mItem(aItem)
+    , mComp(aComp)
+  {}
+  template<class T>
+  int operator()(const T& aElement) const {
+    if (mComp.Equals(aElement, mItem)) {
+      return 0;
+    }
+
+    return mComp.LessThan(aElement, mItem) ? 1 : -1;
+  }
+};
+
+template<class Item, class Comparator>
+struct ItemComparatorFirstElementGT
+{
+  const Item& mItem;
+  const Comparator& mComp;
+  ItemComparatorFirstElementGT(const Item& aItem, const Comparator& aComp)
+    : mItem(aItem)
+    , mComp(aComp)
+  {}
+  template<class T>
+  int operator()(const T& aElement) const {
+    if (mComp.LessThan(aElement, mItem) ||
+        mComp.Equals(aElement, mItem)) {
+      return 1;
+    } else {
+      return -1;
+    }
+  }
+};
+
+} // namespace detail
+
+//
+// nsTArray_Impl contains most of the guts supporting nsTArray, FallibleTArray,
+// AutoTArray.
+//
+// The only situation in which you might need to use nsTArray_Impl in your code
+// is if you're writing code which mutates a TArray which may or may not be
+// infallible.
+//
+// Code which merely reads from a TArray which may or may not be infallible can
+// simply cast the TArray to |const nsTArray&|; both fallible and infallible
+// TArrays can be cast to |const nsTArray&|.
+//
+template<class E, class Alloc>
+class nsTArray_Impl
+  : public nsTArray_base<Alloc, typename nsTArray_CopyChooser<E>::Type>
+  , public nsTArray_TypedBase<E, nsTArray_Impl<E, Alloc>>
+{
+private:
+  typedef nsTArrayFallibleAllocator FallibleAlloc;
+  typedef nsTArrayInfallibleAllocator InfallibleAlloc;
+
+public:
+  typedef typename nsTArray_CopyChooser<E>::Type     copy_type;
+  typedef nsTArray_base<Alloc, copy_type>            base_type;
+  typedef typename base_type::size_type              size_type;
+  typedef typename base_type::index_type             index_type;
+  typedef E                                          elem_type;
+  typedef nsTArray_Impl<E, Alloc>                    self_type;
+  typedef nsTArrayElementTraits<E>                   elem_traits;
+  typedef nsTArray_SafeElementAtHelper<E, self_type> safeelementat_helper_type;
+  typedef elem_type*                                 iterator;
+  typedef const elem_type*                           const_iterator;
+  typedef mozilla::ReverseIterator<elem_type*>       reverse_iterator;
+  typedef mozilla::ReverseIterator<const elem_type*> const_reverse_iterator;
+
+  using safeelementat_helper_type::SafeElementAt;
+  using base_type::EmptyHdr;
+
+  // A special value that is used to indicate an invalid or unknown index
+  // into the array.
+  static const index_type NoIndex = index_type(-1);
+
+  using base_type::Length;
+
+  //
+  // Finalization method
+  //
+
+  ~nsTArray_Impl() { Clear(); }
+
+  //
+  // Initialization methods
+  //
+
+  nsTArray_Impl() {}
+
+  // Initialize this array and pre-allocate some number of elements.
+  explicit nsTArray_Impl(size_type aCapacity) { SetCapacity(aCapacity); }
+
+  // Initialize this array with an r-value.
+  // Allow different types of allocators, since the allocator doesn't matter.
+  template<typename Allocator>
+  explicit nsTArray_Impl(nsTArray_Impl<E, Allocator>&& aOther)
+  {
+    SwapElements(aOther);
+  }
+
+  // The array's copy-constructor performs a 'deep' copy of the given array.
+  // @param aOther The array object to copy.
+  //
+  // It's very important that we declare this method as taking |const
+  // self_type&| as opposed to taking |const nsTArray_Impl<E, OtherAlloc>| for
+  // an arbitrary OtherAlloc.
+  //
+  // If we don't declare a constructor taking |const self_type&|, C++ generates
+  // a copy-constructor for this class which merely copies the object's
+  // members, which is obviously wrong.
+  //
+  // You can pass an nsTArray_Impl<E, OtherAlloc> to this method because
+  // nsTArray_Impl<E, X> can be cast to const nsTArray_Impl<E, Y>&.  So the
+  // effect on the API is the same as if we'd declared this method as taking
+  // |const nsTArray_Impl<E, OtherAlloc>&|.
+  explicit nsTArray_Impl(const self_type& aOther) { AppendElements(aOther); }
+
+  explicit nsTArray_Impl(std::initializer_list<E> aIL) { AppendElements(aIL.begin(), aIL.size()); }
+  // Allow converting to a const array with a different kind of allocator,
+  // Since the allocator doesn't matter for const arrays
+  template<typename Allocator>
+  operator const nsTArray_Impl<E, Allocator>&() const
+  {
+    return *reinterpret_cast<const nsTArray_Impl<E, Allocator>*>(this);
+  }
+  // And we have to do this for our subclasses too
+  operator const nsTArray<E>&() const
+  {
+    return *reinterpret_cast<const InfallibleTArray<E>*>(this);
+  }
+  operator const FallibleTArray<E>&() const
+  {
+    return *reinterpret_cast<const FallibleTArray<E>*>(this);
+  }
+
+  // The array's assignment operator performs a 'deep' copy of the given
+  // array.  It is optimized to reuse existing storage if possible.
+  // @param aOther The array object to copy.
+  self_type& operator=(const self_type& aOther)
+  {
+    if (this != &aOther) {
+      ReplaceElementsAt(0, Length(), aOther.Elements(), aOther.Length());
+    }
+    return *this;
+  }
+
+  // The array's move assignment operator steals the underlying data from
+  // the other array.
+  // @param other  The array object to move from.
+  self_type& operator=(self_type&& aOther)
+  {
+    if (this != &aOther) {
+      Clear();
+      SwapElements(aOther);
+    }
+    return *this;
+  }
+
+  // Return true if this array has the same length and the same
+  // elements as |aOther|.
+  template<typename Allocator>
+  bool operator==(const nsTArray_Impl<E, Allocator>& aOther) const
+  {
+    size_type len = Length();
+    if (len != aOther.Length()) {
+      return false;
+    }
+
+    // XXX std::equal would be as fast or faster here
+    for (index_type i = 0; i < len; ++i) {
+      if (!(operator[](i) == aOther[i])) {
+        return false;
+      }
+    }
+
+    return true;
+  }
+
+  // Return true if this array does not have the same length and the same
+  // elements as |aOther|.
+  bool operator!=(const self_type& aOther) const { return !operator==(aOther); }
+
+  template<typename Allocator>
+  self_type& operator=(const nsTArray_Impl<E, Allocator>& aOther)
+  {
+    ReplaceElementsAt(0, Length(), aOther.Elements(), aOther.Length());
+    return *this;
+  }
+
+  template<typename Allocator>
+  self_type& operator=(nsTArray_Impl<E, Allocator>&& aOther)
+  {
+    Clear();
+    SwapElements(aOther);
+    return *this;
+  }
+
+  // @return The amount of memory used by this nsTArray_Impl, excluding
+  // sizeof(*this). If you want to measure anything hanging off the array, you
+  // must iterate over the elements and measure them individually; hence the
+  // "Shallow" prefix.
+  size_t ShallowSizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const
+  {
+    if (this->UsesAutoArrayBuffer() || Hdr() == EmptyHdr()) {
+      return 0;
+    }
+    return aMallocSizeOf(this->Hdr());
+  }
+
+  // @return The amount of memory used by this nsTArray_Impl, including
+  // sizeof(*this). If you want to measure anything hanging off the array, you
+  // must iterate over the elements and measure them individually; hence the
+  // "Shallow" prefix.
+  size_t ShallowSizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const
+  {
+    return aMallocSizeOf(this) + ShallowSizeOfExcludingThis(aMallocSizeOf);
+  }
+
+  //
+  // Accessor methods
+  //
+
+  // This method provides direct access to the array elements.
+  // @return A pointer to the first element of the array.  If the array is
+  // empty, then this pointer must not be dereferenced.
+  elem_type* Elements() { return reinterpret_cast<elem_type*>(Hdr() + 1); }
+
+  // This method provides direct, readonly access to the array elements.
+  // @return A pointer to the first element of the array.  If the array is
+  // empty, then this pointer must not be dereferenced.
+  const elem_type* Elements() const
+  {
+    return reinterpret_cast<const elem_type*>(Hdr() + 1);
+  }
+
+  // This method provides direct access to an element of the array. The given
+  // index must be within the array bounds.
+  // @param aIndex The index of an element in the array.
+  // @return A reference to the i'th element of the array.
+  elem_type& ElementAt(index_type aIndex)
+  {
+    if (MOZ_UNLIKELY(aIndex >= Length())) {
+      InvalidArrayIndex_CRASH(aIndex, Length());
+    }
+    return Elements()[aIndex];
+  }
+
+  // This method provides direct, readonly access to an element of the array
+  // The given index must be within the array bounds.
+  // @param aIndex The index of an element in the array.
+  // @return A const reference to the i'th element of the array.
+  const elem_type& ElementAt(index_type aIndex) const
+  {
+    if (MOZ_UNLIKELY(aIndex >= Length())) {
+      InvalidArrayIndex_CRASH(aIndex, Length());
+    }
+    return Elements()[aIndex];
+  }
+
+  // This method provides direct access to an element of the array in a bounds
+  // safe manner. If the requested index is out of bounds the provided default
+  // value is returned.
+  // @param aIndex The index of an element in the array.
+  // @param aDef   The value to return if the index is out of bounds.
+  elem_type& SafeElementAt(index_type aIndex, elem_type& aDef)
+  {
+    return aIndex < Length() ? Elements()[aIndex] : aDef;
+  }
+
+  // This method provides direct access to an element of the array in a bounds
+  // safe manner. If the requested index is out of bounds the provided default
+  // value is returned.
+  // @param aIndex The index of an element in the array.
+  // @param aDef   The value to return if the index is out of bounds.
+  const elem_type& SafeElementAt(index_type aIndex, const elem_type& aDef) const
+  {
+    return aIndex < Length() ? Elements()[aIndex] : aDef;
+  }
+
+  // Shorthand for ElementAt(aIndex)
+  elem_type& operator[](index_type aIndex) { return ElementAt(aIndex); }
+
+  // Shorthand for ElementAt(aIndex)
+  const elem_type& operator[](index_type aIndex) const { return ElementAt(aIndex); }
+
+  // Shorthand for ElementAt(length - 1)
+  elem_type& LastElement() { return ElementAt(Length() - 1); }
+
+  // Shorthand for ElementAt(length - 1)
+  const elem_type& LastElement() const { return ElementAt(Length() - 1); }
+
+  // Shorthand for SafeElementAt(length - 1, def)
+  elem_type& SafeLastElement(elem_type& aDef)
+  {
+    return SafeElementAt(Length() - 1, aDef);
+  }
+
+  // Shorthand for SafeElementAt(length - 1, def)
+  const elem_type& SafeLastElement(const elem_type& aDef) const
+  {
+    return SafeElementAt(Length() - 1, aDef);
+  }
+
+  // Methods for range-based for loops.
+  iterator begin() { return Elements(); }
+  const_iterator begin() const { return Elements(); }
+  const_iterator cbegin() const { return begin(); }
+  iterator end() { return Elements() + Length(); }
+  const_iterator end() const { return Elements() + Length(); }
+  const_iterator cend() const { return end(); }
+
+  // Methods for reverse iterating.
+  reverse_iterator rbegin() { return reverse_iterator(end()); }
+  const_reverse_iterator rbegin() const { return const_reverse_iterator(end()); }
+  const_reverse_iterator crbegin() const { return rbegin(); }
+  reverse_iterator rend() { return reverse_iterator(begin()); }
+  const_reverse_iterator rend() const { return const_reverse_iterator(begin()); }
+  const_reverse_iterator crend() const { return rend(); }
+
+  //
+  // Search methods
+  //
+
+  // This method searches for the first element in this array that is equal
+  // to the given element.
+  // @param aItem  The item to search for.
+  // @param aComp  The Comparator used to determine element equality.
+  // @return       true if the element was found.
+  template<class Item, class Comparator>
+  bool Contains(const Item& aItem, const Comparator& aComp) const
+  {
+    return IndexOf(aItem, 0, aComp) != NoIndex;
+  }
+
+  // This method searches for the first element in this array that is equal
+  // to the given element.  This method assumes that 'operator==' is defined
+  // for elem_type.
+  // @param aItem  The item to search for.
+  // @return       true if the element was found.
+  template<class Item>
+  bool Contains(const Item& aItem) const
+  {
+    return IndexOf(aItem) != NoIndex;
+  }
+
+  // This method searches for the offset of the first element in this
+  // array that is equal to the given element.
+  // @param aItem  The item to search for.
+  // @param aStart The index to start from.
+  // @param aComp  The Comparator used to determine element equality.
+  // @return       The index of the found element or NoIndex if not found.
+  template<class Item, class Comparator>
+  index_type IndexOf(const Item& aItem, index_type aStart,
+                     const Comparator& aComp) const
+  {
+    const elem_type* iter = Elements() + aStart;
+    const elem_type* iend = Elements() + Length();
+    for (; iter != iend; ++iter) {
+      if (aComp.Equals(*iter, aItem)) {
+        return index_type(iter - Elements());
+      }
+    }
+    return NoIndex;
+  }
+
+  // This method searches for the offset of the first element in this
+  // array that is equal to the given element.  This method assumes
+  // that 'operator==' is defined for elem_type.
+  // @param aItem  The item to search for.
+  // @param aStart The index to start from.
+  // @return       The index of the found element or NoIndex if not found.
+  template<class Item>
+  index_type IndexOf(const Item& aItem, index_type aStart = 0) const
+  {
+    return IndexOf(aItem, aStart, nsDefaultComparator<elem_type, Item>());
+  }
+
+  // This method searches for the offset of the last element in this
+  // array that is equal to the given element.
+  // @param aItem  The item to search for.
+  // @param aStart The index to start from.  If greater than or equal to the
+  //               length of the array, then the entire array is searched.
+  // @param aComp  The Comparator used to determine element equality.
+  // @return       The index of the found element or NoIndex if not found.
+  template<class Item, class Comparator>
+  index_type LastIndexOf(const Item& aItem, index_type aStart,
+                         const Comparator& aComp) const
+  {
+    size_type endOffset = aStart >= Length() ? Length() : aStart + 1;
+    const elem_type* iend = Elements() - 1;
+    const elem_type* iter = iend + endOffset;
+    for (; iter != iend; --iter) {
+      if (aComp.Equals(*iter, aItem)) {
+        return index_type(iter - Elements());
+      }
+    }
+    return NoIndex;
+  }
+
+  // This method searches for the offset of the last element in this
+  // array that is equal to the given element.  This method assumes
+  // that 'operator==' is defined for elem_type.
+  // @param aItem  The item to search for.
+  // @param aStart The index to start from.  If greater than or equal to the
+  //               length of the array, then the entire array is searched.
+  // @return       The index of the found element or NoIndex if not found.
+  template<class Item>
+  index_type LastIndexOf(const Item& aItem,
+                         index_type aStart = NoIndex) const
+  {
+    return LastIndexOf(aItem, aStart, nsDefaultComparator<elem_type, Item>());
+  }
+
+  // This method searches for the offset for the element in this array
+  // that is equal to the given element. The array is assumed to be sorted.
+  // If there is more than one equivalent element, there is no guarantee
+  // on which one will be returned.
+  // @param aItem  The item to search for.
+  // @param aComp  The Comparator used.
+  // @return       The index of the found element or NoIndex if not found.
+  template<class Item, class Comparator>
+  index_type BinaryIndexOf(const Item& aItem, const Comparator& aComp) const
+  {
+    using mozilla::BinarySearchIf;
+    typedef ::detail::ItemComparatorEq<Item, Comparator> Cmp;
+
+    size_t index;
+    bool found = BinarySearchIf(*this, 0, Length(), Cmp(aItem, aComp), &index);
+    return found ? index : NoIndex;
+  }
+
+  // This method searches for the offset for the element in this array
+  // that is equal to the given element. The array is assumed to be sorted.
+  // This method assumes that 'operator==' and 'operator<' are defined.
+  // @param aItem  The item to search for.
+  // @return       The index of the found element or NoIndex if not found.
+  template<class Item>
+  index_type BinaryIndexOf(const Item& aItem) const
+  {
+    return BinaryIndexOf(aItem, nsDefaultComparator<elem_type, Item>());
+  }
+
+  //
+  // Mutation methods
+  //
+
+  template<class Allocator, typename ActualAlloc = Alloc>
+  typename ActualAlloc::ResultType Assign(
+      const nsTArray_Impl<E, Allocator>& aOther)
+  {
+    return ActualAlloc::ConvertBoolToResultType(
+      !!ReplaceElementsAt<E, ActualAlloc>(0, Length(),
+                                          aOther.Elements(), aOther.Length()));
+  }
+
+  template<class Allocator>
+  MOZ_MUST_USE
+  bool Assign(const nsTArray_Impl<E, Allocator>& aOther,
+              const mozilla::fallible_t&)
+  {
+    return Assign<Allocator, FallibleAlloc>(aOther);
+  }
+
+  template<class Allocator>
+  void Assign(nsTArray_Impl<E, Allocator>&& aOther)
+  {
+    Clear();
+    SwapElements(aOther);
+  }
+
+  // This method call the destructor on each element of the array, empties it,
+  // but does not shrink the array's capacity.
+  // See also SetLengthAndRetainStorage.
+  // Make sure to call Compact() if needed to avoid keeping a huge array
+  // around.
+  void ClearAndRetainStorage()
+  {
+    if (base_type::mHdr == EmptyHdr()) {
+      return;
+    }
+
+    DestructRange(0, Length());
+    base_type::mHdr->mLength = 0;
+  }
+
+  // This method modifies the length of the array, but unlike SetLength
+  // it doesn't deallocate/reallocate the current internal storage.
+  // The new length MUST be shorter than or equal to the current capacity.
+  // If the new length is larger than the existing length of the array,
+  // then new elements will be constructed using elem_type's default
+  // constructor.  If shorter, elements will be destructed and removed.
+  // See also ClearAndRetainStorage.
+  // @param aNewLen  The desired length of this array.
+  void SetLengthAndRetainStorage(size_type aNewLen)
+  {
+    MOZ_ASSERT(aNewLen <= base_type::Capacity());
+    size_type oldLen = Length();
+    if (aNewLen > oldLen) {
+      InsertElementsAt(oldLen, aNewLen - oldLen);
+      return;
+    }
+    if (aNewLen < oldLen) {
+      DestructRange(aNewLen, oldLen - aNewLen);
+      base_type::mHdr->mLength = aNewLen;
+    }
+  }
+
+  // This method replaces a range of elements in this array.
+  // @param aStart    The starting index of the elements to replace.
+  // @param aCount    The number of elements to replace.  This may be zero to
+  //                  insert elements without removing any existing elements.
+  // @param aArray    The values to copy into this array.  Must be non-null,
+  //                  and these elements must not already exist in the array
+  //                  being modified.
+  // @param aArrayLen The number of values to copy into this array.
+  // @return          A pointer to the new elements in the array, or null if
+  //                  the operation failed due to insufficient memory.
+protected:
+  template<class Item, typename ActualAlloc = Alloc>
+  elem_type* ReplaceElementsAt(index_type aStart, size_type aCount,
+                               const Item* aArray, size_type aArrayLen);
+
+public:
+
+  template<class Item>
+  MOZ_MUST_USE
+  elem_type* ReplaceElementsAt(index_type aStart, size_type aCount,
+                               const Item* aArray, size_type aArrayLen,
+                               const mozilla::fallible_t&)
+  {
+    return ReplaceElementsAt<Item, FallibleAlloc>(aStart, aCount,
+                                                  aArray, aArrayLen);
+  }
+
+  // A variation on the ReplaceElementsAt method defined above.
+protected:
+  template<class Item, typename ActualAlloc = Alloc>
+  elem_type* ReplaceElementsAt(index_type aStart, size_type aCount,
+                               const nsTArray<Item>& aArray)
+  {
+    return ReplaceElementsAt<Item, ActualAlloc>(
+      aStart, aCount, aArray.Elements(), aArray.Length());
+  }
+public:
+
+  template<class Item>
+  MOZ_MUST_USE
+  elem_type* ReplaceElementsAt(index_type aStart, size_type aCount,
+                               const nsTArray<Item>& aArray,
+                               const mozilla::fallible_t&)
+  {
+    return ReplaceElementsAt<Item, FallibleAlloc>(aStart, aCount, aArray);
+  }
+
+  // A variation on the ReplaceElementsAt method defined above.
+protected:
+  template<class Item, typename ActualAlloc = Alloc>
+  elem_type* ReplaceElementsAt(index_type aStart, size_type aCount,
+                               const Item& aItem)
+  {
+    return ReplaceElementsAt<Item, ActualAlloc>(aStart, aCount, &aItem, 1);
+  }
+public:
+
+  template<class Item>
+  MOZ_MUST_USE
+  elem_type* ReplaceElementsAt(index_type aStart, size_type aCount,
+                               const Item& aItem, const mozilla::fallible_t&)
+  {
+    return ReplaceElementsAt<Item, FallibleAlloc>(aStart, aCount, aItem);
+  }
+
+  // A variation on the ReplaceElementsAt method defined above.
+  template<class Item>
+  elem_type* ReplaceElementAt(index_type aIndex, const Item& aItem)
+  {
+    return ReplaceElementsAt(aIndex, 1, &aItem, 1);
+  }
+
+  // A variation on the ReplaceElementsAt method defined above.
+protected:
+  template<class Item, typename ActualAlloc = Alloc>
+  elem_type* InsertElementsAt(index_type aIndex, const Item* aArray,
+                              size_type aArrayLen)
+  {
+    return ReplaceElementsAt<Item, ActualAlloc>(aIndex, 0, aArray, aArrayLen);
+  }
+public:
+
+  template<class Item>
+  MOZ_MUST_USE
+  elem_type* InsertElementsAt(index_type aIndex, const Item* aArray,
+                              size_type aArrayLen, const mozilla::fallible_t&)
+  {
+    return InsertElementsAt<Item, FallibleAlloc>(aIndex, aArray, aArrayLen);
+  }
+
+  // A variation on the ReplaceElementsAt method defined above.
+protected:
+  template<class Item, class Allocator, typename ActualAlloc = Alloc>
+  elem_type* InsertElementsAt(index_type aIndex,
+                              const nsTArray_Impl<Item, Allocator>& aArray)
+  {
+    return ReplaceElementsAt<Item, ActualAlloc>(
+      aIndex, 0, aArray.Elements(), aArray.Length());
+  }
+public:
+
+  template<class Item, class Allocator>
+  MOZ_MUST_USE
+  elem_type* InsertElementsAt(index_type aIndex,
+                              const nsTArray_Impl<Item, Allocator>& aArray,
+                              const mozilla::fallible_t&)
+  {
+    return InsertElementsAt<Item, Allocator, FallibleAlloc>(aIndex, aArray);
+  }
+
+  // Insert a new element without copy-constructing. This is useful to avoid
+  // temporaries.
+  // @return A pointer to the newly inserted element, or null on OOM.
+protected:
+  template<typename ActualAlloc = Alloc>
+  elem_type* InsertElementAt(index_type aIndex);
+
+public:
+
+  MOZ_MUST_USE
+  elem_type* InsertElementAt(index_type aIndex, const mozilla::fallible_t&)
+  {
+    return InsertElementAt<FallibleAlloc>(aIndex);
+  }
+
+  // Insert a new element, move constructing if possible.
+protected:
+  template<class Item, typename ActualAlloc = Alloc>
+  elem_type* InsertElementAt(index_type aIndex, Item&& aItem);
+
+public:
+
+  template<class Item>
+  MOZ_MUST_USE
+  elem_type* InsertElementAt(index_type aIndex, Item&& aItem,
+                             const mozilla::fallible_t&)
+  {
+    return InsertElementAt<Item, FallibleAlloc>(aIndex,
+                                                mozilla::Forward<Item>(aItem));
+  }
+
+  // This method searches for the smallest index of an element that is strictly
+  // greater than |aItem|. If |aItem| is inserted at this index, the array will
+  // remain sorted and |aItem| would come after all elements that are equal to
+  // it. If |aItem| is greater than or equal to all elements in the array, the
+  // array length is returned.
+  //
+  // Note that consumers who want to know whether there are existing items equal
+  // to |aItem| in the array can just check that the return value here is > 0
+  // and indexing into the previous slot gives something equal to |aItem|.
+  //
+  //
+  // @param aItem  The item to search for.
+  // @param aComp  The Comparator used.
+  // @return        The index of greatest element <= to |aItem|
+  // @precondition The array is sorted
+  template<class Item, class Comparator>
+  index_type IndexOfFirstElementGt(const Item& aItem,
+                                   const Comparator& aComp) const
+  {
+    using mozilla::BinarySearchIf;
+    typedef ::detail::ItemComparatorFirstElementGT<Item, Comparator> Cmp;
+
+    size_t index;
+    BinarySearchIf(*this, 0, Length(), Cmp(aItem, aComp), &index);
+    return index;
+  }
+
+  // A variation on the IndexOfFirstElementGt method defined above.
+  template<class Item>
+  index_type
+  IndexOfFirstElementGt(const Item& aItem) const
+  {
+    return IndexOfFirstElementGt(aItem, nsDefaultComparator<elem_type, Item>());
+  }
+
+  // Inserts |aItem| at such an index to guarantee that if the array
+  // was previously sorted, it will remain sorted after this
+  // insertion.
+protected:
+  template<class Item, class Comparator, typename ActualAlloc = Alloc>
+  elem_type* InsertElementSorted(Item&& aItem, const Comparator& aComp)
+  {
+    index_type index = IndexOfFirstElementGt<Item, Comparator>(aItem, aComp);
+    return InsertElementAt<Item, ActualAlloc>(
+      index, mozilla::Forward<Item>(aItem));
+  }
+public:
+
+  template<class Item, class Comparator>
+  MOZ_MUST_USE
+  elem_type* InsertElementSorted(Item&& aItem, const Comparator& aComp,
+                                 const mozilla::fallible_t&)
+  {
+    return InsertElementSorted<Item, Comparator, FallibleAlloc>(
+      mozilla::Forward<Item>(aItem), aComp);
+  }
+
+  // A variation on the InsertElementSorted method defined above.
+protected:
+  template<class Item, typename ActualAlloc = Alloc>
+  elem_type* InsertElementSorted(Item&& aItem)
+  {
+    nsDefaultComparator<elem_type, Item> comp;
+    return InsertElementSorted<Item, decltype(comp), ActualAlloc>(
+      mozilla::Forward<Item>(aItem), comp);
+  }
+public:
+
+  template<class Item>
+  MOZ_MUST_USE
+  elem_type* InsertElementSorted(Item&& aItem, const mozilla::fallible_t&)
+  {
+    return InsertElementSorted<Item, FallibleAlloc>(
+      mozilla::Forward<Item>(aItem));
+  }
+
+  // This method appends elements to the end of this array.
+  // @param aArray    The elements to append to this array.
+  // @param aArrayLen The number of elements to append to this array.
+  // @return          A pointer to the new elements in the array, or null if
+  //                  the operation failed due to insufficient memory.
+protected:
+  template<class Item, typename ActualAlloc = Alloc>
+  elem_type* AppendElements(const Item* aArray, size_type aArrayLen);
+
+public:
+
+  template<class Item>
+  /* MOZ_MUST_USE */
+  elem_type* AppendElements(const Item* aArray, size_type aArrayLen,
+                            const mozilla::fallible_t&)
+  {
+    return AppendElements<Item, FallibleAlloc>(aArray, aArrayLen);
+  }
+
+  // A variation on the AppendElements method defined above.
+protected:
+  template<class Item, class Allocator, typename ActualAlloc = Alloc>
+  elem_type* AppendElements(const nsTArray_Impl<Item, Allocator>& aArray)
+  {
+    return AppendElements<Item, ActualAlloc>(aArray.Elements(), aArray.Length());
+  }
+public:
+
+  template<class Item, class Allocator>
+  /* MOZ_MUST_USE */
+  elem_type* AppendElements(const nsTArray_Impl<Item, Allocator>& aArray,
+                            const mozilla::fallible_t&)
+  {
+    return AppendElements<Item, Allocator, FallibleAlloc>(aArray);
+  }
+
+  // Move all elements from another array to the end of this array.
+  // @return A pointer to the newly appended elements, or null on OOM.
+protected:
+  template<class Item, class Allocator, typename ActualAlloc = Alloc>
+  elem_type* AppendElements(nsTArray_Impl<Item, Allocator>&& aArray);
+
+public:
+
+  template<class Item, class Allocator, typename ActualAlloc = Alloc>
+  /* MOZ_MUST_USE */
+  elem_type* AppendElements(nsTArray_Impl<Item, Allocator>&& aArray,
+                            const mozilla::fallible_t&)
+  {
+    return AppendElements<Item, Allocator>(mozilla::Move(aArray));
+  }
+
+  // Append a new element, move constructing if possible.
+protected:
+  template<class Item, typename ActualAlloc = Alloc>
+  elem_type* AppendElement(Item&& aItem);
+
+public:
+
+  template<class Item>
+  /* MOZ_MUST_USE */
+  elem_type* AppendElement(Item&& aItem,
+                           const mozilla::fallible_t&)
+  {
+    return AppendElement<Item, FallibleAlloc>(mozilla::Forward<Item>(aItem));
+  }
+
+  // Append new elements without copy-constructing. This is useful to avoid
+  // temporaries.
+  // @return A pointer to the newly appended elements, or null on OOM.
+protected:
+  template<typename ActualAlloc = Alloc>
+  elem_type* AppendElements(size_type aCount) {
+    if (!ActualAlloc::Successful(this->template EnsureCapacity<ActualAlloc>(
+          Length() + aCount, sizeof(elem_type)))) {
+      return nullptr;
+    }
+    elem_type* elems = Elements() + Length();
+    size_type i;
+    for (i = 0; i < aCount; ++i) {
+      elem_traits::Construct(elems + i);
+    }
+    this->IncrementLength(aCount);
+    return elems;
+  }
+public:
+
+  /* MOZ_MUST_USE */
+  elem_type* AppendElements(size_type aCount,
+                            const mozilla::fallible_t&)
+  {
+    return AppendElements<FallibleAlloc>(aCount);
+  }
+
+  // Append a new element without copy-constructing. This is useful to avoid
+  // temporaries.
+  // @return A pointer to the newly appended element, or null on OOM.
+protected:
+  template<typename ActualAlloc = Alloc>
+  elem_type* AppendElement()
+  {
+    return AppendElements<ActualAlloc>(1);
+  }
+public:
+
+  /* MOZ_MUST_USE */
+  elem_type* AppendElement(const mozilla::fallible_t&)
+  {
+    return AppendElement<FallibleAlloc>();
+  }
+
+  // This method removes a range of elements from this array.
+  // @param aStart The starting index of the elements to remove.
+  // @param aCount The number of elements to remove.
+  void RemoveElementsAt(index_type aStart, size_type aCount);
+
+  // A variation on the RemoveElementsAt method defined above.
+  void RemoveElementAt(index_type aIndex) { RemoveElementsAt(aIndex, 1); }
+
+  // A variation on the RemoveElementsAt method defined above.
+  void Clear() { RemoveElementsAt(0, Length()); }
+
+  // This method removes elements based on the return value of the
+  // callback function aPredicate. If the function returns true for
+  // an element, the element is removed. aPredicate will be called
+  // for each element in order. It is not safe to access the array
+  // inside aPredicate.
+  template<typename Predicate>
+  void RemoveElementsBy(Predicate aPredicate);
+
+  // This helper function combines IndexOf with RemoveElementAt to "search
+  // and destroy" the first element that is equal to the given element.
+  // @param aItem The item to search for.
+  // @param aComp The Comparator used to determine element equality.
+  // @return true if the element was found
+  template<class Item, class Comparator>
+  bool RemoveElement(const Item& aItem, const Comparator& aComp)
+  {
+    index_type i = IndexOf(aItem, 0, aComp);
+    if (i == NoIndex) {
+      return false;
+    }
+
+    RemoveElementAt(i);
+    return true;
+  }
+
+  // A variation on the RemoveElement method defined above that assumes
+  // that 'operator==' is defined for elem_type.
+  template<class Item>
+  bool RemoveElement(const Item& aItem)
+  {
+    return RemoveElement(aItem, nsDefaultComparator<elem_type, Item>());
+  }
+
+  // This helper function combines IndexOfFirstElementGt with
+  // RemoveElementAt to "search and destroy" the last element that
+  // is equal to the given element.
+  // @param aItem The item to search for.
+  // @param aComp The Comparator used to determine element equality.
+  // @return true if the element was found
+  template<class Item, class Comparator>
+  bool RemoveElementSorted(const Item& aItem, const Comparator& aComp)
+  {
+    index_type index = IndexOfFirstElementGt(aItem, aComp);
+    if (index > 0 && aComp.Equals(ElementAt(index - 1), aItem)) {
+      RemoveElementAt(index - 1);
+      return true;
+    }
+    return false;
+  }
+
+  // A variation on the RemoveElementSorted method defined above.
+  template<class Item>
+  bool RemoveElementSorted(const Item& aItem)
+  {
+    return RemoveElementSorted(aItem, nsDefaultComparator<elem_type, Item>());
+  }
+
+  // This method causes the elements contained in this array and the given
+  // array to be swapped.
+  template<class Allocator>
+  typename Alloc::ResultType SwapElements(nsTArray_Impl<E, Allocator>& aOther)
+  {
+    return Alloc::Result(this->template SwapArrayElements<Alloc>(
+      aOther, sizeof(elem_type), MOZ_ALIGNOF(elem_type)));
+  }
+
+  //
+  // Allocation
+  //
+
+  // This method may increase the capacity of this array object by the
+  // specified amount.  This method may be called in advance of several
+  // AppendElement operations to minimize heap re-allocations.  This method
+  // will not reduce the number of elements in this array.
+  // @param aCapacity The desired capacity of this array.
+  // @return True if the operation succeeded; false if we ran out of memory
+protected:
+  template<typename ActualAlloc = Alloc>
+  typename ActualAlloc::ResultType SetCapacity(size_type aCapacity)
+  {
+    return ActualAlloc::Result(this->template EnsureCapacity<ActualAlloc>(
+      aCapacity, sizeof(elem_type)));
+  }
+public:
+
+  MOZ_MUST_USE
+  bool SetCapacity(size_type aCapacity, const mozilla::fallible_t&)
+  {
+    return SetCapacity<FallibleAlloc>(aCapacity);
+  }
+
+  // This method modifies the length of the array.  If the new length is
+  // larger than the existing length of the array, then new elements will be
+  // constructed using elem_type's default constructor.  Otherwise, this call
+  // removes elements from the array (see also RemoveElementsAt).
+  // @param aNewLen The desired length of this array.
+  // @return True if the operation succeeded; false otherwise.
+  // See also TruncateLength if the new length is guaranteed to be smaller than
+  // the old.
+protected:
+  template<typename ActualAlloc = Alloc>
+  typename ActualAlloc::ResultType SetLength(size_type aNewLen)
+  {
+    size_type oldLen = Length();
+    if (aNewLen > oldLen) {
+      return ActualAlloc::ConvertBoolToResultType(
+        InsertElementsAt<ActualAlloc>(oldLen, aNewLen - oldLen) != nullptr);
+    }
+
+    TruncateLength(aNewLen);
+    return ActualAlloc::ConvertBoolToResultType(true);
+  }
+public:
+
+  MOZ_MUST_USE
+  bool SetLength(size_type aNewLen, const mozilla::fallible_t&)
+  {
+    return SetLength<FallibleAlloc>(aNewLen);
+  }
+
+  // This method modifies the length of the array, but may only be
+  // called when the new length is shorter than the old.  It can
+  // therefore be called when elem_type has no default constructor,
+  // unlike SetLength.  It removes elements from the array (see also
+  // RemoveElementsAt).
+  // @param aNewLen The desired length of this array.
+  void TruncateLength(size_type aNewLen)
+  {
+    size_type oldLen = Length();
+    MOZ_ASSERT(aNewLen <= oldLen,
+               "caller should use SetLength instead");
+    RemoveElementsAt(aNewLen, oldLen - aNewLen);
+  }
+
+  // This method ensures that the array has length at least the given
+  // length.  If the current length is shorter than the given length,
+  // then new elements will be constructed using elem_type's default
+  // constructor.
+  // @param aMinLen The desired minimum length of this array.
+  // @return True if the operation succeeded; false otherwise.
+protected:
+  template<typename ActualAlloc = Alloc>
+  typename ActualAlloc::ResultType EnsureLengthAtLeast(size_type aMinLen)
+  {
+    size_type oldLen = Length();
+    if (aMinLen > oldLen) {
+      return ActualAlloc::ConvertBoolToResultType(
+        !!InsertElementsAt<ActualAlloc>(oldLen, aMinLen - oldLen));
+    }
+    return ActualAlloc::ConvertBoolToResultType(true);
+  }
+public:
+
+  MOZ_MUST_USE
+  bool EnsureLengthAtLeast(size_type aMinLen, const mozilla::fallible_t&)
+  {
+    return EnsureLengthAtLeast<FallibleAlloc>(aMinLen);
+  }
+
+  // This method inserts elements into the array, constructing
+  // them using elem_type's default constructor.
+  // @param aIndex the place to insert the new elements. This must be no
+  //               greater than the current length of the array.
+  // @param aCount the number of elements to insert
+protected:
+  template<typename ActualAlloc = Alloc>
+  elem_type* InsertElementsAt(index_type aIndex, size_type aCount)
+  {
+    if (!base_type::template InsertSlotsAt<ActualAlloc>(aIndex, aCount,
+                                                        sizeof(elem_type),
+                                                        MOZ_ALIGNOF(elem_type))) {
+      return nullptr;
+    }
+
+    // Initialize the extra array elements
+    elem_type* iter = Elements() + aIndex;
+    elem_type* iend = iter + aCount;
+    for (; iter != iend; ++iter) {
+      elem_traits::Construct(iter);
+    }
+
+    return Elements() + aIndex;
+  }
+public:
+
+  MOZ_MUST_USE
+  elem_type* InsertElementsAt(index_type aIndex, size_type aCount,
+                              const mozilla::fallible_t&)
+  {
+    return InsertElementsAt<FallibleAlloc>(aIndex, aCount);
+  }
+
+  // This method inserts elements into the array, constructing them
+  // elem_type's copy constructor (or whatever one-arg constructor
+  // happens to match the Item type).
+  // @param aIndex the place to insert the new elements. This must be no
+  //               greater than the current length of the array.
+  // @param aCount the number of elements to insert.
+  // @param aItem the value to use when constructing the new elements.
+protected:
+  template<class Item, typename ActualAlloc = Alloc>
+  elem_type* InsertElementsAt(index_type aIndex, size_type aCount,
+                              const Item& aItem);
+
+public:
+
+  template<class Item>
+  MOZ_MUST_USE
+  elem_type* InsertElementsAt(index_type aIndex, size_type aCount,
+                              const Item& aItem, const mozilla::fallible_t&)
+  {
+    return InsertElementsAt<Item, FallibleAlloc>(aIndex, aCount, aItem);
+  }
+
+  // This method may be called to minimize the memory used by this array.
+  void Compact()
+  {
+    ShrinkCapacity(sizeof(elem_type), MOZ_ALIGNOF(elem_type));
+  }
+
+  //
+  // Sorting
+  //
+
+  // This function is meant to be used with the NS_QuickSort function.  It
+  // maps the callback API expected by NS_QuickSort to the Comparator API
+  // used by nsTArray_Impl.  See nsTArray_Impl::Sort.
+  template<class Comparator>
+  static int Compare(const void* aE1, const void* aE2, void* aData)
+  {
+    const Comparator* c = reinterpret_cast<const Comparator*>(aData);
+    const elem_type* a = static_cast<const elem_type*>(aE1);
+    const elem_type* b = static_cast<const elem_type*>(aE2);
+    return c->LessThan(*a, *b) ? -1 : (c->Equals(*a, *b) ? 0 : 1);
+  }
+
+  // This method sorts the elements of the array.  It uses the LessThan
+  // method defined on the given Comparator object to collate elements.
+  // @param aComp The Comparator used to collate elements.
+  template<class Comparator>
+  void Sort(const Comparator& aComp)
+  {
+    NS_QuickSort(Elements(), Length(), sizeof(elem_type),
+                 Compare<Comparator>, const_cast<Comparator*>(&aComp));
+  }
+
+  // A variation on the Sort method defined above that assumes that
+  // 'operator<' is defined for elem_type.
+  void Sort() { Sort(nsDefaultComparator<elem_type, elem_type>()); }
+
+protected:
+  using base_type::Hdr;
+  using base_type::ShrinkCapacity;
+
+  // This method invokes elem_type's destructor on a range of elements.
+  // @param aStart The index of the first element to destroy.
+  // @param aCount The number of elements to destroy.
+  void DestructRange(index_type aStart, size_type aCount)
+  {
+    elem_type* iter = Elements() + aStart;
+    elem_type *iend = iter + aCount;
+    for (; iter != iend; ++iter) {
+      elem_traits::Destruct(iter);
+    }
+  }
+
+  // This method invokes elem_type's copy-constructor on a range of elements.
+  // @param aStart  The index of the first element to construct.
+  // @param aCount  The number of elements to construct.
+  // @param aValues The array of elements to copy.
+  template<class Item>
+  void AssignRange(index_type aStart, size_type aCount, const Item* aValues)
+  {
+    AssignRangeAlgorithm<mozilla::IsPod<Item>::value,
+                         mozilla::IsSame<Item, elem_type>::value>
+                         ::implementation(Elements(), aStart, aCount, aValues);
+  }
+};
+
+template<typename E, class Alloc>
+template<class Item, typename ActualAlloc>
+auto
+nsTArray_Impl<E, Alloc>::ReplaceElementsAt(index_type aStart, size_type aCount,
+                                           const Item* aArray, size_type aArrayLen) -> elem_type*
+{
+  // Adjust memory allocation up-front to catch errors.
+  if (!ActualAlloc::Successful(this->template EnsureCapacity<ActualAlloc>(
+        Length() + aArrayLen - aCount, sizeof(elem_type)))) {
+    return nullptr;
+  }
+  DestructRange(aStart, aCount);
+  this->template ShiftData<ActualAlloc>(aStart, aCount, aArrayLen,
+                                        sizeof(elem_type),
+                                        MOZ_ALIGNOF(elem_type));
+  AssignRange(aStart, aArrayLen, aArray);
+  return Elements() + aStart;
+}
+
+template<typename E, class Alloc>
+void
+nsTArray_Impl<E, Alloc>::RemoveElementsAt(index_type aStart, size_type aCount)
+{
+  MOZ_ASSERT(aCount == 0 || aStart < Length(), "Invalid aStart index");
+  MOZ_ASSERT(aStart + aCount <= Length(), "Invalid length");
+  // Check that the previous assert didn't overflow
+  MOZ_ASSERT(aStart <= aStart + aCount, "Start index plus length overflows");
+  DestructRange(aStart, aCount);
+  this->template ShiftData<InfallibleAlloc>(aStart, aCount, 0,
+                                            sizeof(elem_type),
+                                            MOZ_ALIGNOF(elem_type));
+}
+
+template<typename E, class Alloc>
+template<typename Predicate>
+void
+nsTArray_Impl<E, Alloc>::RemoveElementsBy(Predicate aPredicate)
+{
+  if (base_type::mHdr == EmptyHdr()) {
+    return;
+  }
+
+  index_type j = 0;
+  index_type len = Length();
+  for (index_type i = 0; i < len; ++i) {
+    if (aPredicate(Elements()[i])) {
+      elem_traits::Destruct(Elements() + i);
+    } else {
+      if (j < i) {
+        copy_type::MoveNonOverlappingRegion(Elements() + j, Elements() + i,
+                                            1, sizeof(elem_type));
+      }
+      ++j;
+    }
+  }
+  base_type::mHdr->mLength = j;
+}
+
+template<typename E, class Alloc>
+template<class Item, typename ActualAlloc>
+auto
+nsTArray_Impl<E, Alloc>::InsertElementsAt(index_type aIndex, size_type aCount,
+                                          const Item& aItem) -> elem_type*
+{
+  if (!base_type::template InsertSlotsAt<ActualAlloc>(aIndex, aCount,
+                                                      sizeof(elem_type),
+                                                      MOZ_ALIGNOF(elem_type))) {
+    return nullptr;
+  }
+
+  // Initialize the extra array elements
+  elem_type* iter = Elements() + aIndex;
+  elem_type* iend = iter + aCount;
+  for (; iter != iend; ++iter) {
+    elem_traits::Construct(iter, aItem);
+  }
+
+  return Elements() + aIndex;
+}
+
+template<typename E, class Alloc>
+template<typename ActualAlloc>
+auto
+nsTArray_Impl<E, Alloc>::InsertElementAt(index_type aIndex) -> elem_type*
+{
+  if (!ActualAlloc::Successful(this->template EnsureCapacity<ActualAlloc>(
+        Length() + 1, sizeof(elem_type)))) {
+    return nullptr;
+  }
+  this->template ShiftData<ActualAlloc>(aIndex, 0, 1, sizeof(elem_type),
+                                        MOZ_ALIGNOF(elem_type));
+  elem_type* elem = Elements() + aIndex;
+  elem_traits::Construct(elem);
+  return elem;
+}
+
+template<typename E, class Alloc>
+template<class Item, typename ActualAlloc>
+auto
+nsTArray_Impl<E, Alloc>::InsertElementAt(index_type aIndex, Item&& aItem) -> elem_type*
+{
+  if (!ActualAlloc::Successful(this->template EnsureCapacity<ActualAlloc>(
+         Length() + 1, sizeof(elem_type)))) {
+    return nullptr;
+  }
+  this->template ShiftData<ActualAlloc>(aIndex, 0, 1, sizeof(elem_type),
+                                        MOZ_ALIGNOF(elem_type));
+  elem_type* elem = Elements() + aIndex;
+  elem_traits::Construct(elem, mozilla::Forward<Item>(aItem));
+  return elem;
+}
+
+template<typename E, class Alloc>
+template<class Item, typename ActualAlloc>
+auto
+nsTArray_Impl<E, Alloc>::AppendElements(const Item* aArray, size_type aArrayLen) -> elem_type*
+{
+  if (!ActualAlloc::Successful(this->template EnsureCapacity<ActualAlloc>(
+        Length() + aArrayLen, sizeof(elem_type)))) {
+    return nullptr;
+  }
+  index_type len = Length();
+  AssignRange(len, aArrayLen, aArray);
+  this->IncrementLength(aArrayLen);
+  return Elements() + len;
+}
+
+template<typename E, class Alloc>
+template<class Item, class Allocator, typename ActualAlloc>
+auto
+nsTArray_Impl<E, Alloc>::AppendElements(nsTArray_Impl<Item, Allocator>&& aArray) -> elem_type*
+{
+  MOZ_ASSERT(&aArray != this, "argument must be different aArray");
+  if (Length() == 0) {
+    SwapElements<ActualAlloc>(aArray);
+    return Elements();
+  }
+
+  index_type len = Length();
+  index_type otherLen = aArray.Length();
+  if (!Alloc::Successful(this->template EnsureCapacity<Alloc>(
+        len + otherLen, sizeof(elem_type)))) {
+    return nullptr;
+  }
+  copy_type::MoveNonOverlappingRegion(Elements() + len, aArray.Elements(), otherLen,
+                                      sizeof(elem_type));
+  this->IncrementLength(otherLen);
+  aArray.template ShiftData<Alloc>(0, otherLen, 0, sizeof(elem_type),
+                                   MOZ_ALIGNOF(elem_type));
+  return Elements() + len;
+}
+
+template<typename E, class Alloc>
+template<class Item, typename ActualAlloc>
+auto
+nsTArray_Impl<E, Alloc>::AppendElement(Item&& aItem) -> elem_type*
+{
+  if (!ActualAlloc::Successful(this->template EnsureCapacity<ActualAlloc>(
+         Length() + 1, sizeof(elem_type)))) {
+    return nullptr;
+  }
+  elem_type* elem = Elements() + Length();
+  elem_traits::Construct(elem, mozilla::Forward<Item>(aItem));
+  this->IncrementLength(1);
+  return elem;
+}
+
+template<typename E, typename Alloc>
+inline void
+ImplCycleCollectionUnlink(nsTArray_Impl<E, Alloc>& aField)
+{
+  aField.Clear();
+}
+
+template<typename E, typename Alloc>
+inline void
+ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
+                            nsTArray_Impl<E, Alloc>& aField,
+                            const char* aName,
+                            uint32_t aFlags = 0)
+{
+  aFlags |= CycleCollectionEdgeNameArrayFlag;
+  size_t length = aField.Length();
+  for (size_t i = 0; i < length; ++i) {
+    ImplCycleCollectionTraverse(aCallback, aField[i], aName, aFlags);
+  }
+}
+
+//
+// nsTArray is an infallible vector class.  See the comment at the top of this
+// file for more details.
+//
+template<class E>
+class nsTArray : public nsTArray_Impl<E, nsTArrayInfallibleAllocator>
+{
+public:
+  typedef nsTArray_Impl<E, nsTArrayInfallibleAllocator> base_type;
+  typedef nsTArray<E>                                   self_type;
+  typedef typename base_type::size_type                 size_type;
+
+  nsTArray() {}
+  explicit nsTArray(size_type aCapacity) : base_type(aCapacity) {}
+  explicit nsTArray(const nsTArray& aOther) : base_type(aOther) {}
+  MOZ_IMPLICIT nsTArray(nsTArray&& aOther) : base_type(mozilla::Move(aOther)) {}
+  MOZ_IMPLICIT nsTArray(std::initializer_list<E> aIL) : base_type(aIL) {}
+
+  template<class Allocator>
+  explicit nsTArray(const nsTArray_Impl<E, Allocator>& aOther)
+    : base_type(aOther)
+  {
+  }
+  template<class Allocator>
+  MOZ_IMPLICIT nsTArray(nsTArray_Impl<E, Allocator>&& aOther)
+    : base_type(mozilla::Move(aOther))
+  {
+  }
+
+  self_type& operator=(const self_type& aOther)
+  {
+    base_type::operator=(aOther);
+    return *this;
+  }
+  template<class Allocator>
+  self_type& operator=(const nsTArray_Impl<E, Allocator>& aOther)
+  {
+    base_type::operator=(aOther);
+    return *this;
+  }
+  self_type& operator=(self_type&& aOther)
+  {
+    base_type::operator=(mozilla::Move(aOther));
+    return *this;
+  }
+  template<class Allocator>
+  self_type& operator=(nsTArray_Impl<E, Allocator>&& aOther)
+  {
+    base_type::operator=(mozilla::Move(aOther));
+    return *this;
+  }
+
+  using base_type::AppendElement;
+  using base_type::AppendElements;
+  using base_type::EnsureLengthAtLeast;
+  using base_type::InsertElementAt;
+  using base_type::InsertElementsAt;
+  using base_type::InsertElementSorted;
+  using base_type::ReplaceElementsAt;
+  using base_type::SetCapacity;
+  using base_type::SetLength;
+};
+
+//
+// FallibleTArray is a fallible vector class.
+//
+template<class E>
+class FallibleTArray : public nsTArray_Impl<E, nsTArrayFallibleAllocator>
+{
+public:
+  typedef nsTArray_Impl<E, nsTArrayFallibleAllocator>   base_type;
+  typedef FallibleTArray<E>                             self_type;
+  typedef typename base_type::size_type                 size_type;
+
+  FallibleTArray() {}
+  explicit FallibleTArray(size_type aCapacity) : base_type(aCapacity) {}
+  explicit FallibleTArray(const FallibleTArray<E>& aOther) : base_type(aOther) {}
+  FallibleTArray(FallibleTArray<E>&& aOther)
+    : base_type(mozilla::Move(aOther))
+  {
+  }
+
+  template<class Allocator>
+  explicit FallibleTArray(const nsTArray_Impl<E, Allocator>& aOther)
+    : base_type(aOther)
+  {
+  }
+  template<class Allocator>
+  explicit FallibleTArray(nsTArray_Impl<E, Allocator>&& aOther)
+    : base_type(mozilla::Move(aOther))
+  {
+  }
+
+  self_type& operator=(const self_type& aOther)
+  {
+    base_type::operator=(aOther);
+    return *this;
+  }
+  template<class Allocator>
+  self_type& operator=(const nsTArray_Impl<E, Allocator>& aOther)
+  {
+    base_type::operator=(aOther);
+    return *this;
+  }
+  self_type& operator=(self_type&& aOther)
+  {
+    base_type::operator=(mozilla::Move(aOther));
+    return *this;
+  }
+  template<class Allocator>
+  self_type& operator=(nsTArray_Impl<E, Allocator>&& aOther)
+  {
+    base_type::operator=(mozilla::Move(aOther));
+    return *this;
+  }
+};
+
+//
+// AutoTArray<E, N> is like nsTArray<E>, but with N elements of inline storage.
+// Storing more than N elements is fine, but it will cause a heap allocation.
+//
+template<class E, size_t N>
+class MOZ_NON_MEMMOVABLE AutoTArray : public nsTArray<E>
+{
+  static_assert(N != 0, "AutoTArray<E, 0> should be specialized");
+public:
+  typedef AutoTArray<E, N> self_type;
+  typedef nsTArray<E> base_type;
+  typedef typename base_type::Header Header;
+  typedef typename base_type::elem_type elem_type;
+
+  AutoTArray()
+  {
+    Init();
+  }
+
+  AutoTArray(const self_type& aOther)
+  {
+    Init();
+    this->AppendElements(aOther);
+  }
+
+  explicit AutoTArray(const base_type& aOther)
+  {
+    Init();
+    this->AppendElements(aOther);
+  }
+
+  explicit AutoTArray(base_type&& aOther)
+  {
+    Init();
+    this->SwapElements(aOther);
+  }
+
+  template<typename Allocator>
+  explicit AutoTArray(nsTArray_Impl<elem_type, Allocator>&& aOther)
+  {
+    Init();
+    this->SwapElements(aOther);
+  }
+
+  MOZ_IMPLICIT AutoTArray(std::initializer_list<E> aIL)
+  {
+    Init();
+    this->AppendElements(aIL.begin(), aIL.size());
+  }
+
+  self_type& operator=(const self_type& aOther)
+  {
+    base_type::operator=(aOther);
+    return *this;
+  }
+
+  template<typename Allocator>
+  self_type& operator=(const nsTArray_Impl<elem_type, Allocator>& aOther)
+  {
+    base_type::operator=(aOther);
+    return *this;
+  }
+
+private:
+  // nsTArray_base casts itself as an nsAutoArrayBase in order to get a pointer
+  // to mAutoBuf.
+  template<class Allocator, class Copier>
+  friend class nsTArray_base;
+
+  void Init()
+  {
+    static_assert(MOZ_ALIGNOF(elem_type) <= 8,
+                  "can't handle alignments greater than 8, "
+                  "see nsTArray_base::UsesAutoArrayBuffer()");
+    // Temporary work around for VS2012 RC compiler crash
+    Header** phdr = base_type::PtrToHdr();
+    *phdr = reinterpret_cast<Header*>(&mAutoBuf);
+    (*phdr)->mLength = 0;
+    (*phdr)->mCapacity = N;
+    (*phdr)->mIsAutoArray = 1;
+
+    MOZ_ASSERT(base_type::GetAutoArrayBuffer(MOZ_ALIGNOF(elem_type)) ==
+               reinterpret_cast<Header*>(&mAutoBuf),
+               "GetAutoArrayBuffer needs to be fixed");
+  }
+
+  // Declare mAutoBuf aligned to the maximum of the header's alignment and
+  // elem_type's alignment.  We need to use a union rather than
+  // MOZ_ALIGNED_DECL because GCC is picky about what goes into
+  // __attribute__((aligned(foo))).
+  union
+  {
+    char mAutoBuf[sizeof(nsTArrayHeader) + N * sizeof(elem_type)];
+    // Do the max operation inline to ensure that it is a compile-time constant.
+    mozilla::AlignedElem<(MOZ_ALIGNOF(Header) > MOZ_ALIGNOF(elem_type)) ?
+                         MOZ_ALIGNOF(Header) : MOZ_ALIGNOF(elem_type)> mAlign;
+  };
+};
+
+//
+// Specialization of AutoTArray<E, N> for the case where N == 0.
+// AutoTArray<E, 0> behaves exactly like nsTArray<E>, but without this
+// specialization, it stores a useless inline header.
+//
+// We do have many AutoTArray<E, 0> objects in memory: about 2,000 per tab as
+// of May 2014. These are typically not explicitly AutoTArray<E, 0> but rather
+// AutoTArray<E, N> for some value N depending on template parameters, in
+// generic code.
+//
+// For that reason, we optimize this case with the below partial specialization,
+// which ensures that AutoTArray<E, 0> is just like nsTArray<E>, without any
+// inline header overhead.
+//
+template<class E>
+class AutoTArray<E, 0> : public nsTArray<E>
+{
+};
+
+template<class E, size_t N>
+struct nsTArray_CopyChooser<AutoTArray<E, N>>
+{
+  typedef nsTArray_CopyWithConstructors<AutoTArray<E, N>> Type;
+};
+
+// Assert that AutoTArray doesn't have any extra padding inside.
+//
+// It's important that the data stored in this auto array takes up a multiple of
+// 8 bytes; e.g. AutoTArray<uint32_t, 1> wouldn't work.  Since AutoTArray
+// contains a pointer, its size must be a multiple of alignof(void*).  (This is
+// because any type may be placed into an array, and there's no padding between
+// elements of an array.)  The compiler pads the end of the structure to
+// enforce this rule.
+//
+// If we used AutoTArray<uint32_t, 1> below, this assertion would fail on a
+// 64-bit system, where the compiler inserts 4 bytes of padding at the end of
+// the auto array to make its size a multiple of alignof(void*) == 8 bytes.
+
+static_assert(sizeof(AutoTArray<uint32_t, 2>) ==
+              sizeof(void*) + sizeof(nsTArrayHeader) + sizeof(uint32_t) * 2,
+              "AutoTArray shouldn't contain any extra padding, "
+              "see the comment");
+
+// Definitions of nsTArray_Impl methods
+#include "nsTArray-inl.h"
+
+#endif  // nsTArray_h__