Add m-esr52 at 52.6.0

1 files changed, 1932 insertions, 0 deletions

diff --git a/docshell/shistory/nsSHistory.cpp b/docshell/shistory/nsSHistory.cpp
new file mode 100644
index 000000000..7c148ffcc
--- /dev/null
+++ b/docshell/shistory/nsSHistory.cpp
@@ -0,0 +1,1932 @@
+/* -*- 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/. */
+
+#include "nsSHistory.h"
+#include <algorithm>
+
+// Helper Classes
+#include "mozilla/Preferences.h"
+#include "mozilla/StaticPtr.h"
+
+// Interfaces Needed
+#include "nsILayoutHistoryState.h"
+#include "nsIDocShell.h"
+#include "nsIDocShellLoadInfo.h"
+#include "nsISHContainer.h"
+#include "nsIDocShellTreeItem.h"
+#include "nsIURI.h"
+#include "nsIContentViewer.h"
+#include "nsIObserverService.h"
+#include "prclist.h"
+#include "mozilla/Services.h"
+#include "nsTArray.h"
+#include "nsCOMArray.h"
+#include "nsDocShell.h"
+#include "mozilla/Attributes.h"
+#include "nsISHEntry.h"
+#include "nsISHTransaction.h"
+#include "nsISHistoryListener.h"
+#include "nsComponentManagerUtils.h"
+
+// For calculating max history entries and max cachable contentviewers
+#include "prsystem.h"
+#include "mozilla/MathAlgorithms.h"
+
+using namespace mozilla;
+
+#define PREF_SHISTORY_SIZE "browser.sessionhistory.max_entries"
+#define PREF_SHISTORY_MAX_TOTAL_VIEWERS "browser.sessionhistory.max_total_viewers"
+
+static const char* kObservedPrefs[] = {
+  PREF_SHISTORY_SIZE,
+  PREF_SHISTORY_MAX_TOTAL_VIEWERS,
+  nullptr
+};
+
+static int32_t gHistoryMaxSize = 50;
+// Max viewers allowed per SHistory objects
+static const int32_t gHistoryMaxViewers = 3;
+// List of all SHistory objects, used for content viewer cache eviction
+static PRCList gSHistoryList;
+// Max viewers allowed total, across all SHistory objects - negative default
+// means we will calculate how many viewers to cache based on total memory
+int32_t nsSHistory::sHistoryMaxTotalViewers = -1;
+
+// A counter that is used to be able to know the order in which
+// entries were touched, so that we can evict older entries first.
+static uint32_t gTouchCounter = 0;
+
+static LazyLogModule gSHistoryLog("nsSHistory");
+
+#define LOG(format) MOZ_LOG(gSHistoryLog, mozilla::LogLevel::Debug, format)
+
+// This macro makes it easier to print a log message which includes a URI's
+// spec.  Example use:
+//
+//  nsIURI *uri = [...];
+//  LOG_SPEC(("The URI is %s.", _spec), uri);
+//
+#define LOG_SPEC(format, uri)                              \
+  PR_BEGIN_MACRO                                           \
+    if (MOZ_LOG_TEST(gSHistoryLog, LogLevel::Debug)) {     \
+      nsAutoCString _specStr(NS_LITERAL_CSTRING("(null)"));\
+      if (uri) {                                           \
+        _specStr = uri->GetSpecOrDefault();                \
+      }                                                    \
+      const char* _spec = _specStr.get();                  \
+      LOG(format);                                         \
+    }                                                      \
+  PR_END_MACRO
+
+// This macro makes it easy to log a message including an SHEntry's URI.
+// For example:
+//
+//  nsCOMPtr<nsISHEntry> shentry = [...];
+//  LOG_SHENTRY_SPEC(("shentry %p has uri %s.", shentry.get(), _spec), shentry);
+//
+#define LOG_SHENTRY_SPEC(format, shentry)                  \
+  PR_BEGIN_MACRO                                           \
+    if (MOZ_LOG_TEST(gSHistoryLog, LogLevel::Debug)) {     \
+      nsCOMPtr<nsIURI> uri;                                \
+      shentry->GetURI(getter_AddRefs(uri));                \
+      LOG_SPEC(format, uri);                               \
+    }                                                      \
+  PR_END_MACRO
+
+// Iterates over all registered session history listeners.
+#define ITERATE_LISTENERS(body)                            \
+  PR_BEGIN_MACRO                                           \
+  {                                                        \
+    nsAutoTObserverArray<nsWeakPtr, 2>::EndLimitedIterator \
+      iter(mListeners);                                    \
+    while (iter.HasMore()) {                               \
+      nsCOMPtr<nsISHistoryListener> listener =             \
+        do_QueryReferent(iter.GetNext());                  \
+      if (listener) {                                      \
+        body                                               \
+      }                                                    \
+    }                                                      \
+  }                                                        \
+  PR_END_MACRO
+
+// Calls a given method on all registered session history listeners.
+#define NOTIFY_LISTENERS(method, args)                     \
+  ITERATE_LISTENERS(                                       \
+    listener->method args;                                 \
+  );
+
+// Calls a given method on all registered session history listeners.
+// Listeners may return 'false' to cancel an action so make sure that we
+// set the return value to 'false' if one of the listeners wants to cancel.
+#define NOTIFY_LISTENERS_CANCELABLE(method, retval, args)  \
+  PR_BEGIN_MACRO                                           \
+  {                                                        \
+    bool canceled = false;                                 \
+    retval = true;                                         \
+    ITERATE_LISTENERS(                                     \
+      listener->method args;                               \
+      if (!retval) {                                       \
+        canceled = true;                                   \
+      }                                                    \
+    );                                                     \
+    if (canceled) {                                        \
+      retval = false;                                      \
+    }                                                      \
+  }                                                        \
+  PR_END_MACRO
+
+enum HistCmd
+{
+  HIST_CMD_BACK,
+  HIST_CMD_FORWARD,
+  HIST_CMD_GOTOINDEX,
+  HIST_CMD_RELOAD
+};
+
+class nsSHistoryObserver final : public nsIObserver
+{
+public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  nsSHistoryObserver() {}
+
+protected:
+  ~nsSHistoryObserver() {}
+};
+
+StaticRefPtr<nsSHistoryObserver> gObserver;
+
+NS_IMPL_ISUPPORTS(nsSHistoryObserver, nsIObserver)
+
+NS_IMETHODIMP
+nsSHistoryObserver::Observe(nsISupports* aSubject, const char* aTopic,
+                            const char16_t* aData)
+{
+  if (!strcmp(aTopic, NS_PREFBRANCH_PREFCHANGE_TOPIC_ID)) {
+    nsSHistory::UpdatePrefs();
+    nsSHistory::GloballyEvictContentViewers();
+  } else if (!strcmp(aTopic, "cacheservice:empty-cache") ||
+             !strcmp(aTopic, "memory-pressure")) {
+    nsSHistory::GloballyEvictAllContentViewers();
+  }
+
+  return NS_OK;
+}
+
+namespace {
+
+already_AddRefed<nsIContentViewer>
+GetContentViewerForTransaction(nsISHTransaction* aTrans)
+{
+  nsCOMPtr<nsISHEntry> entry;
+  aTrans->GetSHEntry(getter_AddRefs(entry));
+  if (!entry) {
+    return nullptr;
+  }
+
+  nsCOMPtr<nsISHEntry> ownerEntry;
+  nsCOMPtr<nsIContentViewer> viewer;
+  entry->GetAnyContentViewer(getter_AddRefs(ownerEntry),
+                             getter_AddRefs(viewer));
+  return viewer.forget();
+}
+
+void
+EvictContentViewerForTransaction(nsISHTransaction* aTrans)
+{
+  nsCOMPtr<nsISHEntry> entry;
+  aTrans->GetSHEntry(getter_AddRefs(entry));
+  nsCOMPtr<nsIContentViewer> viewer;
+  nsCOMPtr<nsISHEntry> ownerEntry;
+  entry->GetAnyContentViewer(getter_AddRefs(ownerEntry),
+                             getter_AddRefs(viewer));
+  if (viewer) {
+    NS_ASSERTION(ownerEntry, "Content viewer exists but its SHEntry is null");
+
+    LOG_SHENTRY_SPEC(("Evicting content viewer 0x%p for "
+                      "owning SHEntry 0x%p at %s.",
+                      viewer.get(), ownerEntry.get(), _spec),
+                     ownerEntry);
+
+    // Drop the presentation state before destroying the viewer, so that
+    // document teardown is able to correctly persist the state.
+    ownerEntry->SetContentViewer(nullptr);
+    ownerEntry->SyncPresentationState();
+    viewer->Destroy();
+  }
+}
+
+} // namespace
+
+nsSHistory::nsSHistory()
+  : mIndex(-1)
+  , mLength(0)
+  , mRequestedIndex(-1)
+  , mIsPartial(false)
+  , mGlobalIndexOffset(0)
+  , mEntriesInFollowingPartialHistories(0)
+  , mRootDocShell(nullptr)
+{
+  // Add this new SHistory object to the list
+  PR_APPEND_LINK(this, &gSHistoryList);
+}
+
+nsSHistory::~nsSHistory()
+{
+  // Remove this SHistory object from the list
+  PR_REMOVE_LINK(this);
+}
+
+NS_IMPL_ADDREF(nsSHistory)
+NS_IMPL_RELEASE(nsSHistory)
+
+NS_INTERFACE_MAP_BEGIN(nsSHistory)
+  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsISHistory)
+  NS_INTERFACE_MAP_ENTRY(nsISHistory)
+  NS_INTERFACE_MAP_ENTRY(nsIWebNavigation)
+  NS_INTERFACE_MAP_ENTRY(nsISHistoryInternal)
+NS_INTERFACE_MAP_END
+
+// static
+uint32_t
+nsSHistory::CalcMaxTotalViewers()
+{
+  // Calculate an estimate of how many ContentViewers we should cache based
+  // on RAM.  This assumes that the average ContentViewer is 4MB (conservative)
+  // and caps the max at 8 ContentViewers
+  //
+  // TODO: Should we split the cache memory betw. ContentViewer caching and
+  // nsCacheService?
+  //
+  // RAM      ContentViewers
+  // -----------------------
+  // 32   Mb       0
+  // 64   Mb       1
+  // 128  Mb       2
+  // 256  Mb       3
+  // 512  Mb       5
+  // 1024 Mb       8
+  // 2048 Mb       8
+  // 4096 Mb       8
+  uint64_t bytes = PR_GetPhysicalMemorySize();
+
+  if (bytes == 0) {
+    return 0;
+  }
+
+  // Conversion from unsigned int64_t to double doesn't work on all platforms.
+  // We need to truncate the value at INT64_MAX to make sure we don't
+  // overflow.
+  if (bytes > INT64_MAX) {
+    bytes = INT64_MAX;
+  }
+
+  double kBytesD = (double)(bytes >> 10);
+
+  // This is essentially the same calculation as for nsCacheService,
+  // except that we divide the final memory calculation by 4, since
+  // we assume each ContentViewer takes on average 4MB
+  uint32_t viewers = 0;
+  double x = std::log(kBytesD) / std::log(2.0) - 14;
+  if (x > 0) {
+    viewers = (uint32_t)(x * x - x + 2.001); // add .001 for rounding
+    viewers /= 4;
+  }
+
+  // Cap it off at 8 max
+  if (viewers > 8) {
+    viewers = 8;
+  }
+  return viewers;
+}
+
+// static
+void
+nsSHistory::UpdatePrefs()
+{
+  Preferences::GetInt(PREF_SHISTORY_SIZE, &gHistoryMaxSize);
+  Preferences::GetInt(PREF_SHISTORY_MAX_TOTAL_VIEWERS,
+                      &sHistoryMaxTotalViewers);
+  // If the pref is negative, that means we calculate how many viewers
+  // we think we should cache, based on total memory
+  if (sHistoryMaxTotalViewers < 0) {
+    sHistoryMaxTotalViewers = CalcMaxTotalViewers();
+  }
+}
+
+// static
+nsresult
+nsSHistory::Startup()
+{
+  UpdatePrefs();
+
+  // The goal of this is to unbreak users who have inadvertently set their
+  // session history size to less than the default value.
+  int32_t defaultHistoryMaxSize =
+    Preferences::GetDefaultInt(PREF_SHISTORY_SIZE, 50);
+  if (gHistoryMaxSize < defaultHistoryMaxSize) {
+    gHistoryMaxSize = defaultHistoryMaxSize;
+  }
+
+  // Allow the user to override the max total number of cached viewers,
+  // but keep the per SHistory cached viewer limit constant
+  if (!gObserver) {
+    gObserver = new nsSHistoryObserver();
+    Preferences::AddStrongObservers(gObserver, kObservedPrefs);
+
+    nsCOMPtr<nsIObserverService> obsSvc =
+      mozilla::services::GetObserverService();
+    if (obsSvc) {
+      // Observe empty-cache notifications so tahat clearing the disk/memory
+      // cache will also evict all content viewers.
+      obsSvc->AddObserver(gObserver, "cacheservice:empty-cache", false);
+
+      // Same for memory-pressure notifications
+      obsSvc->AddObserver(gObserver, "memory-pressure", false);
+    }
+  }
+
+  // Initialize the global list of all SHistory objects
+  PR_INIT_CLIST(&gSHistoryList);
+  return NS_OK;
+}
+
+// static
+void
+nsSHistory::Shutdown()
+{
+  if (gObserver) {
+    Preferences::RemoveObservers(gObserver, kObservedPrefs);
+    nsCOMPtr<nsIObserverService> obsSvc =
+      mozilla::services::GetObserverService();
+    if (obsSvc) {
+      obsSvc->RemoveObserver(gObserver, "cacheservice:empty-cache");
+      obsSvc->RemoveObserver(gObserver, "memory-pressure");
+    }
+    gObserver = nullptr;
+  }
+}
+
+/* Add an entry to the History list at mIndex and
+ * increment the index to point to the new entry
+ */
+NS_IMETHODIMP
+nsSHistory::AddEntry(nsISHEntry* aSHEntry, bool aPersist)
+{
+  NS_ENSURE_ARG(aSHEntry);
+
+  nsCOMPtr<nsISHTransaction> currentTxn;
+
+  if (mListRoot) {
+    GetTransactionAtIndex(mIndex, getter_AddRefs(currentTxn));
+  }
+
+  bool currentPersist = true;
+  if (currentTxn) {
+    currentTxn->GetPersist(&currentPersist);
+  }
+
+  int32_t currentIndex = mIndex;
+
+  if (!currentPersist) {
+    NOTIFY_LISTENERS(OnHistoryReplaceEntry, (currentIndex));
+    NS_ENSURE_SUCCESS(currentTxn->SetSHEntry(aSHEntry), NS_ERROR_FAILURE);
+    currentTxn->SetPersist(aPersist);
+    return NS_OK;
+  }
+
+  nsCOMPtr<nsISHTransaction> txn(
+    do_CreateInstance(NS_SHTRANSACTION_CONTRACTID));
+  NS_ENSURE_TRUE(txn, NS_ERROR_FAILURE);
+
+  nsCOMPtr<nsIURI> uri;
+  aSHEntry->GetURI(getter_AddRefs(uri));
+  NOTIFY_LISTENERS(OnHistoryNewEntry, (uri, currentIndex));
+
+  // If a listener has changed mIndex, we need to get currentTxn again,
+  // otherwise we'll be left at an inconsistent state (see bug 320742)
+  if (currentIndex != mIndex) {
+    GetTransactionAtIndex(mIndex, getter_AddRefs(currentTxn));
+  }
+
+  // Set the ShEntry and parent for the transaction. setting the
+  // parent will properly set the parent child relationship
+  txn->SetPersist(aPersist);
+  NS_ENSURE_SUCCESS(txn->Create(aSHEntry, currentTxn), NS_ERROR_FAILURE);
+
+  // A little tricky math here...  Basically when adding an object regardless of
+  // what the length was before, it should always be set back to the current and
+  // lop off the forward.
+  mLength = (++mIndex + 1);
+  NOTIFY_LISTENERS(OnLengthChange, (mLength));
+
+  // Much like how mLength works above, when changing our entries, all following
+  // partial histories should be purged, so we just reset the number to zero.
+  mEntriesInFollowingPartialHistories = 0;
+
+  // If this is the very first transaction, initialize the list
+  if (!mListRoot) {
+    mListRoot = txn;
+  }
+
+  // Purge History list if it is too long
+  if (gHistoryMaxSize >= 0 && mLength > gHistoryMaxSize) {
+    PurgeHistory(mLength - gHistoryMaxSize);
+  }
+
+  RemoveDynEntries(mIndex - 1, mIndex);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::GetIsPartial(bool* aResult)
+{
+  NS_ENSURE_ARG_POINTER(aResult);
+  *aResult = mIsPartial;
+  return NS_OK;
+}
+
+/* Get size of the history list */
+NS_IMETHODIMP
+nsSHistory::GetCount(int32_t* aResult)
+{
+  NS_ENSURE_ARG_POINTER(aResult);
+  *aResult = mLength;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::GetGlobalCount(int32_t* aResult)
+{
+  NS_ENSURE_ARG_POINTER(aResult);
+  *aResult = mGlobalIndexOffset + mLength + mEntriesInFollowingPartialHistories;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::GetGlobalIndexOffset(int32_t* aResult)
+{
+  NS_ENSURE_ARG_POINTER(aResult);
+  *aResult = mGlobalIndexOffset;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::OnPartialSessionHistoryActive(int32_t aGlobalLength, int32_t aTargetIndex)
+{
+  NS_ENSURE_TRUE(mIsPartial, NS_ERROR_UNEXPECTED);
+
+  int32_t extraLength = aGlobalLength - mLength - mGlobalIndexOffset;
+  NS_ENSURE_TRUE(extraLength >= 0, NS_ERROR_UNEXPECTED);
+
+  if (extraLength != mEntriesInFollowingPartialHistories) {
+    mEntriesInFollowingPartialHistories = extraLength;
+  }
+
+  if (mIndex == aTargetIndex) {
+    // TODO When we finish OnPartialSessionHistoryDeactive, we'll need to active
+    // the suspended document here.
+
+    // Fire location change to update canGoBack / canGoForward.
+    NS_DispatchToCurrentThread(NewRunnableMethod(static_cast<nsDocShell*>(mRootDocShell),
+                                                 &nsDocShell::FireDummyOnLocationChange));
+    return NS_OK;
+  }
+
+  return LoadEntry(aTargetIndex, nsIDocShellLoadInfo::loadHistory,
+                   HIST_CMD_GOTOINDEX);
+}
+
+NS_IMETHODIMP
+nsSHistory::OnPartialSessionHistoryDeactive()
+{
+  NS_ENSURE_TRUE(mIsPartial, NS_ERROR_UNEXPECTED);
+
+  // TODO We need to suspend current document first. Much like what happens when
+  // loading a new page. Move the ownership of the document to nsISHEntry or so.
+  return NS_OK;
+}
+
+/* Get index of the history list */
+NS_IMETHODIMP
+nsSHistory::GetIndex(int32_t* aResult)
+{
+  NS_PRECONDITION(aResult, "null out param?");
+  *aResult = mIndex;
+  return NS_OK;
+}
+
+/* Get the requestedIndex */
+NS_IMETHODIMP
+nsSHistory::GetRequestedIndex(int32_t* aResult)
+{
+  NS_PRECONDITION(aResult, "null out param?");
+  *aResult = mRequestedIndex;
+  return NS_OK;
+}
+
+/* Get the entry at a given index */
+NS_IMETHODIMP
+nsSHistory::GetEntryAtIndex(int32_t aIndex, bool aModifyIndex,
+                            nsISHEntry** aResult)
+{
+  nsresult rv;
+  nsCOMPtr<nsISHTransaction> txn;
+
+  /* GetTransactionAtIndex ensures aResult is valid and validates aIndex */
+  rv = GetTransactionAtIndex(aIndex, getter_AddRefs(txn));
+  if (NS_SUCCEEDED(rv) && txn) {
+    // Get the Entry from the transaction
+    rv = txn->GetSHEntry(aResult);
+    if (NS_SUCCEEDED(rv) && (*aResult)) {
+      // Set mIndex to the requested index, if asked to do so..
+      if (aModifyIndex) {
+        mIndex = aIndex;
+      }
+    }
+  }
+  return rv;
+}
+
+/* Get the transaction at a given index */
+NS_IMETHODIMP
+nsSHistory::GetTransactionAtIndex(int32_t aIndex, nsISHTransaction** aResult)
+{
+  nsresult rv;
+  NS_ENSURE_ARG_POINTER(aResult);
+
+  if (mLength <= 0 || aIndex < 0 || aIndex >= mLength) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (!mListRoot) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (aIndex == 0) {
+    *aResult = mListRoot;
+    NS_ADDREF(*aResult);
+    return NS_OK;
+  }
+
+  int32_t cnt = 0;
+  nsCOMPtr<nsISHTransaction> tempPtr;
+  rv = GetRootTransaction(getter_AddRefs(tempPtr));
+  if (NS_FAILED(rv) || !tempPtr) {
+    return NS_ERROR_FAILURE;
+  }
+
+  while (true) {
+    nsCOMPtr<nsISHTransaction> ptr;
+    rv = tempPtr->GetNext(getter_AddRefs(ptr));
+    if (NS_SUCCEEDED(rv) && ptr) {
+      cnt++;
+      if (cnt == aIndex) {
+        ptr.forget(aResult);
+        break;
+      } else {
+        tempPtr = ptr;
+        continue;
+      }
+    } else {
+      return NS_ERROR_FAILURE;
+    }
+  }
+
+  return NS_OK;
+}
+
+/* Get the index of a given entry */
+NS_IMETHODIMP
+nsSHistory::GetIndexOfEntry(nsISHEntry* aSHEntry, int32_t* aResult)
+{
+  NS_ENSURE_ARG(aSHEntry);
+  NS_ENSURE_ARG_POINTER(aResult);
+  *aResult = -1;
+
+  if (mLength <= 0) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsCOMPtr<nsISHTransaction> currentTxn;
+  int32_t cnt = 0;
+
+  nsresult rv = GetRootTransaction(getter_AddRefs(currentTxn));
+  if (NS_FAILED(rv) || !currentTxn) {
+    return NS_ERROR_FAILURE;
+  }
+
+  while (true) {
+    nsCOMPtr<nsISHEntry> entry;
+    rv = currentTxn->GetSHEntry(getter_AddRefs(entry));
+    if (NS_FAILED(rv) || !entry) {
+      return NS_ERROR_FAILURE;
+    }
+
+    if (aSHEntry == entry) {
+      *aResult = cnt;
+      break;
+    }
+
+    rv = currentTxn->GetNext(getter_AddRefs(currentTxn));
+    if (NS_FAILED(rv) || !currentTxn) {
+      return NS_ERROR_FAILURE;
+    }
+
+    cnt++;
+  }
+
+  return NS_OK;
+}
+
+#ifdef DEBUG
+nsresult
+nsSHistory::PrintHistory()
+{
+  nsCOMPtr<nsISHTransaction> txn;
+  int32_t index = 0;
+  nsresult rv;
+
+  if (!mListRoot) {
+    return NS_ERROR_FAILURE;
+  }
+
+  txn = mListRoot;
+
+  while (1) {
+    if (!txn) {
+      break;
+    }
+    nsCOMPtr<nsISHEntry> entry;
+    rv = txn->GetSHEntry(getter_AddRefs(entry));
+    if (NS_FAILED(rv) && !entry) {
+      return NS_ERROR_FAILURE;
+    }
+
+    nsCOMPtr<nsILayoutHistoryState> layoutHistoryState;
+    nsCOMPtr<nsIURI> uri;
+    nsXPIDLString title;
+
+    entry->GetLayoutHistoryState(getter_AddRefs(layoutHistoryState));
+    entry->GetURI(getter_AddRefs(uri));
+    entry->GetTitle(getter_Copies(title));
+
+#if 0
+    nsAutoCString url;
+    if (uri) {
+      uri->GetSpec(url);
+    }
+
+    printf("**** SH Transaction #%d, Entry = %x\n", index, entry.get());
+    printf("\t\t URL = %s\n", url.get());
+
+    printf("\t\t Title = %s\n", NS_LossyConvertUTF16toASCII(title).get());
+    printf("\t\t layout History Data = %x\n", layoutHistoryState.get());
+#endif
+
+    nsCOMPtr<nsISHTransaction> next;
+    rv = txn->GetNext(getter_AddRefs(next));
+    if (NS_SUCCEEDED(rv) && next) {
+      txn = next;
+      index++;
+      continue;
+    } else {
+      break;
+    }
+  }
+
+  return NS_OK;
+}
+#endif
+
+NS_IMETHODIMP
+nsSHistory::GetRootTransaction(nsISHTransaction** aResult)
+{
+  NS_ENSURE_ARG_POINTER(aResult);
+  *aResult = mListRoot;
+  NS_IF_ADDREF(*aResult);
+  return NS_OK;
+}
+
+/* Get the max size of the history list */
+NS_IMETHODIMP
+nsSHistory::GetMaxLength(int32_t* aResult)
+{
+  NS_ENSURE_ARG_POINTER(aResult);
+  *aResult = gHistoryMaxSize;
+  return NS_OK;
+}
+
+/* Set the max size of the history list */
+NS_IMETHODIMP
+nsSHistory::SetMaxLength(int32_t aMaxSize)
+{
+  if (aMaxSize < 0) {
+    return NS_ERROR_ILLEGAL_VALUE;
+  }
+
+  gHistoryMaxSize = aMaxSize;
+  if (mLength > aMaxSize) {
+    PurgeHistory(mLength - aMaxSize);
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::PurgeHistory(int32_t aEntries)
+{
+  if (mLength <= 0 || aEntries <= 0) {
+    return NS_ERROR_FAILURE;
+  }
+
+  aEntries = std::min(aEntries, mLength);
+
+  bool purgeHistory = true;
+  NOTIFY_LISTENERS_CANCELABLE(OnHistoryPurge, purgeHistory,
+                              (aEntries, &purgeHistory));
+
+  if (!purgeHistory) {
+    // Listener asked us not to purge
+    return NS_SUCCESS_LOSS_OF_INSIGNIFICANT_DATA;
+  }
+
+  int32_t cnt = 0;
+  while (cnt < aEntries) {
+    nsCOMPtr<nsISHTransaction> nextTxn;
+    if (mListRoot) {
+      mListRoot->GetNext(getter_AddRefs(nextTxn));
+      mListRoot->SetNext(nullptr);
+    }
+    mListRoot = nextTxn;
+    if (mListRoot) {
+      mListRoot->SetPrev(nullptr);
+    }
+    cnt++;
+  }
+  mLength -= cnt;
+  mIndex -= cnt;
+  NOTIFY_LISTENERS(OnLengthChange, (mLength));
+
+  // All following partial histories will be deleted in this case.
+  mEntriesInFollowingPartialHistories = 0;
+
+  // Now if we were not at the end of the history, mIndex could have
+  // become far too negative.  If so, just set it to -1.
+  if (mIndex < -1) {
+    mIndex = -1;
+  }
+
+  if (mRootDocShell) {
+    mRootDocShell->HistoryPurged(cnt);
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::AddSHistoryListener(nsISHistoryListener* aListener)
+{
+  NS_ENSURE_ARG_POINTER(aListener);
+
+  // Check if the listener supports Weak Reference. This is a must.
+  // This listener functionality is used by embedders and we want to
+  // have the right ownership with who ever listens to SHistory
+  nsWeakPtr listener = do_GetWeakReference(aListener);
+  if (!listener) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return mListeners.AppendElementUnlessExists(listener) ?
+    NS_OK : NS_ERROR_OUT_OF_MEMORY;
+}
+
+NS_IMETHODIMP
+nsSHistory::RemoveSHistoryListener(nsISHistoryListener* aListener)
+{
+  // Make sure the listener that wants to be removed is the
+  // one we have in store.
+  nsWeakPtr listener = do_GetWeakReference(aListener);
+  mListeners.RemoveElement(listener);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::SetPartialSHistoryListener(nsIPartialSHistoryListener* aListener)
+{
+  mPartialHistoryListener = do_GetWeakReference(aListener);
+  return NS_OK;
+}
+
+/* Replace an entry in the History list at a particular index.
+ * Do not update index or count.
+ */
+NS_IMETHODIMP
+nsSHistory::ReplaceEntry(int32_t aIndex, nsISHEntry* aReplaceEntry)
+{
+  NS_ENSURE_ARG(aReplaceEntry);
+  nsresult rv;
+  nsCOMPtr<nsISHTransaction> currentTxn;
+
+  if (!mListRoot) {
+    // Session History is not initialised.
+    return NS_ERROR_FAILURE;
+  }
+
+  rv = GetTransactionAtIndex(aIndex, getter_AddRefs(currentTxn));
+
+  if (currentTxn) {
+    NOTIFY_LISTENERS(OnHistoryReplaceEntry, (aIndex));
+
+    // Set the replacement entry in the transaction
+    rv = currentTxn->SetSHEntry(aReplaceEntry);
+    rv = currentTxn->SetPersist(true);
+  }
+  return rv;
+}
+
+NS_IMETHODIMP
+nsSHistory::NotifyOnHistoryReload(nsIURI* aReloadURI, uint32_t aReloadFlags,
+                                  bool* aCanReload)
+{
+  NOTIFY_LISTENERS_CANCELABLE(OnHistoryReload, *aCanReload,
+                              (aReloadURI, aReloadFlags, aCanReload));
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::EvictOutOfRangeContentViewers(int32_t aIndex)
+{
+  // Check our per SHistory object limit in the currently navigated SHistory
+  EvictOutOfRangeWindowContentViewers(aIndex);
+  // Check our total limit across all SHistory objects
+  GloballyEvictContentViewers();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::EvictAllContentViewers()
+{
+  // XXXbz we don't actually do a good job of evicting things as we should, so
+  // we might have viewers quite far from mIndex.  So just evict everything.
+  nsCOMPtr<nsISHTransaction> trans = mListRoot;
+  while (trans) {
+    EvictContentViewerForTransaction(trans);
+
+    nsCOMPtr<nsISHTransaction> temp = trans;
+    temp->GetNext(getter_AddRefs(trans));
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::GetCanGoBack(bool* aCanGoBack)
+{
+  NS_ENSURE_ARG_POINTER(aCanGoBack);
+
+  if (mGlobalIndexOffset) {
+    *aCanGoBack = true;
+    return NS_OK;
+  }
+
+  int32_t index = -1;
+  NS_ENSURE_SUCCESS(GetIndex(&index), NS_ERROR_FAILURE);
+  if (index > 0) {
+    *aCanGoBack = true;
+    return NS_OK;
+  }
+
+  *aCanGoBack = false;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::GetCanGoForward(bool* aCanGoForward)
+{
+  NS_ENSURE_ARG_POINTER(aCanGoForward);
+
+  if (mEntriesInFollowingPartialHistories) {
+    *aCanGoForward = true;
+    return NS_OK;
+  }
+
+  int32_t index = -1;
+  int32_t count = -1;
+  NS_ENSURE_SUCCESS(GetIndex(&index), NS_ERROR_FAILURE);
+  NS_ENSURE_SUCCESS(GetCount(&count), NS_ERROR_FAILURE);
+  if (index >= 0 && index < (count - 1)) {
+    *aCanGoForward = true;
+    return NS_OK;
+  }
+
+  *aCanGoForward = false;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::GoBack()
+{
+  bool canGoBack = false;
+
+  GetCanGoBack(&canGoBack);
+  if (!canGoBack) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  return LoadEntry(mIndex - 1, nsIDocShellLoadInfo::loadHistory, HIST_CMD_BACK);
+}
+
+NS_IMETHODIMP
+nsSHistory::GoForward()
+{
+  bool canGoForward = false;
+
+  GetCanGoForward(&canGoForward);
+  if (!canGoForward) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  return LoadEntry(mIndex + 1, nsIDocShellLoadInfo::loadHistory,
+                   HIST_CMD_FORWARD);
+}
+
+NS_IMETHODIMP
+nsSHistory::Reload(uint32_t aReloadFlags)
+{
+  nsDocShellInfoLoadType loadType;
+  if (aReloadFlags & nsIWebNavigation::LOAD_FLAGS_BYPASS_PROXY &&
+      aReloadFlags & nsIWebNavigation::LOAD_FLAGS_BYPASS_CACHE) {
+    loadType = nsIDocShellLoadInfo::loadReloadBypassProxyAndCache;
+  } else if (aReloadFlags & nsIWebNavigation::LOAD_FLAGS_BYPASS_PROXY) {
+    loadType = nsIDocShellLoadInfo::loadReloadBypassProxy;
+  } else if (aReloadFlags & nsIWebNavigation::LOAD_FLAGS_BYPASS_CACHE) {
+    loadType = nsIDocShellLoadInfo::loadReloadBypassCache;
+  } else if (aReloadFlags & nsIWebNavigation::LOAD_FLAGS_CHARSET_CHANGE) {
+    loadType = nsIDocShellLoadInfo::loadReloadCharsetChange;
+  } else if (aReloadFlags & nsIWebNavigation::LOAD_FLAGS_ALLOW_MIXED_CONTENT) {
+    loadType = nsIDocShellLoadInfo::loadReloadMixedContent;
+  } else {
+    loadType = nsIDocShellLoadInfo::loadReloadNormal;
+  }
+
+  // We are reloading. Send Reload notifications.
+  // nsDocShellLoadFlagType is not public, where as nsIWebNavigation
+  // is public. So send the reload notifications with the
+  // nsIWebNavigation flags.
+  bool canNavigate = true;
+  nsCOMPtr<nsIURI> currentURI;
+  GetCurrentURI(getter_AddRefs(currentURI));
+  NOTIFY_LISTENERS_CANCELABLE(OnHistoryReload, canNavigate,
+                              (currentURI, aReloadFlags, &canNavigate));
+  if (!canNavigate) {
+    return NS_OK;
+  }
+
+  return LoadEntry(mIndex, loadType, HIST_CMD_RELOAD);
+}
+
+NS_IMETHODIMP
+nsSHistory::ReloadCurrentEntry()
+{
+  // Notify listeners
+  bool canNavigate = true;
+  nsCOMPtr<nsIURI> currentURI;
+  GetCurrentURI(getter_AddRefs(currentURI));
+  NOTIFY_LISTENERS_CANCELABLE(OnHistoryGotoIndex, canNavigate,
+                              (mIndex, currentURI, &canNavigate));
+  if (!canNavigate) {
+    return NS_OK;
+  }
+
+  return LoadEntry(mIndex, nsIDocShellLoadInfo::loadHistory, HIST_CMD_RELOAD);
+}
+
+void
+nsSHistory::EvictOutOfRangeWindowContentViewers(int32_t aIndex)
+{
+  // XXX rename method to EvictContentViewersExceptAroundIndex, or something.
+
+  // We need to release all content viewers that are no longer in the range
+  //
+  //  aIndex - gHistoryMaxViewers to aIndex + gHistoryMaxViewers
+  //
+  // to ensure that this SHistory object isn't responsible for more than
+  // gHistoryMaxViewers content viewers.  But our job is complicated by the
+  // fact that two transactions which are related by either hash navigations or
+  // history.pushState will have the same content viewer.
+  //
+  // To illustrate the issue, suppose gHistoryMaxViewers = 3 and we have four
+  // linked transactions in our history.  Suppose we then add a new content
+  // viewer and call into this function.  So the history looks like:
+  //
+  //   A A A A B
+  //     +     *
+  //
+  // where the letters are content viewers and + and * denote the beginning and
+  // end of the range aIndex +/- gHistoryMaxViewers.
+  //
+  // Although one copy of the content viewer A exists outside the range, we
+  // don't want to evict A, because it has other copies in range!
+  //
+  // We therefore adjust our eviction strategy to read:
+  //
+  //   Evict each content viewer outside the range aIndex -/+
+  //   gHistoryMaxViewers, unless that content viewer also appears within the
+  //   range.
+  //
+  // (Note that it's entirely legal to have two copies of one content viewer
+  // separated by a different content viewer -- call pushState twice, go back
+  // once, and refresh -- so we can't rely on identical viewers only appearing
+  // adjacent to one another.)
+
+  if (aIndex < 0) {
+    return;
+  }
+  NS_ENSURE_TRUE_VOID(aIndex < mLength);
+
+  // Calculate the range that's safe from eviction.
+  int32_t startSafeIndex = std::max(0, aIndex - gHistoryMaxViewers);
+  int32_t endSafeIndex = std::min(mLength, aIndex + gHistoryMaxViewers);
+
+  LOG(("EvictOutOfRangeWindowContentViewers(index=%d), "
+       "mLength=%d. Safe range [%d, %d]",
+       aIndex, mLength, startSafeIndex, endSafeIndex));
+
+  // The content viewers in range aIndex -/+ gHistoryMaxViewers will not be
+  // evicted.  Collect a set of them so we don't accidentally evict one of them
+  // if it appears outside this range.
+  nsCOMArray<nsIContentViewer> safeViewers;
+  nsCOMPtr<nsISHTransaction> trans;
+  GetTransactionAtIndex(startSafeIndex, getter_AddRefs(trans));
+  for (int32_t i = startSafeIndex; trans && i <= endSafeIndex; i++) {
+    nsCOMPtr<nsIContentViewer> viewer = GetContentViewerForTransaction(trans);
+    safeViewers.AppendObject(viewer);
+    nsCOMPtr<nsISHTransaction> temp = trans;
+    temp->GetNext(getter_AddRefs(trans));
+  }
+
+  // Walk the SHistory list and evict any content viewers that aren't safe.
+  GetTransactionAtIndex(0, getter_AddRefs(trans));
+  while (trans) {
+    nsCOMPtr<nsIContentViewer> viewer = GetContentViewerForTransaction(trans);
+    if (safeViewers.IndexOf(viewer) == -1) {
+      EvictContentViewerForTransaction(trans);
+    }
+
+    nsCOMPtr<nsISHTransaction> temp = trans;
+    temp->GetNext(getter_AddRefs(trans));
+  }
+}
+
+namespace {
+
+class TransactionAndDistance
+{
+public:
+  TransactionAndDistance(nsISHTransaction* aTrans, uint32_t aDist)
+    : mTransaction(aTrans)
+    , mLastTouched(0)
+    , mDistance(aDist)
+  {
+    mViewer = GetContentViewerForTransaction(aTrans);
+    NS_ASSERTION(mViewer, "Transaction should have a content viewer");
+
+    nsCOMPtr<nsISHEntry> shentry;
+    mTransaction->GetSHEntry(getter_AddRefs(shentry));
+
+    nsCOMPtr<nsISHEntryInternal> shentryInternal = do_QueryInterface(shentry);
+    if (shentryInternal) {
+      shentryInternal->GetLastTouched(&mLastTouched);
+    } else {
+      NS_WARNING("Can't cast to nsISHEntryInternal?");
+    }
+  }
+
+  bool operator<(const TransactionAndDistance& aOther) const
+  {
+    // Compare distances first, and fall back to last-accessed times.
+    if (aOther.mDistance != this->mDistance) {
+      return this->mDistance < aOther.mDistance;
+    }
+
+    return this->mLastTouched < aOther.mLastTouched;
+  }
+
+  bool operator==(const TransactionAndDistance& aOther) const
+  {
+    // This is a little silly; we need == so the default comaprator can be
+    // instantiated, but this function is never actually called when we sort
+    // the list of TransactionAndDistance objects.
+    return aOther.mDistance == this->mDistance &&
+           aOther.mLastTouched == this->mLastTouched;
+  }
+
+  nsCOMPtr<nsISHTransaction> mTransaction;
+  nsCOMPtr<nsIContentViewer> mViewer;
+  uint32_t mLastTouched;
+  int32_t mDistance;
+};
+
+} // namespace
+
+// static
+void
+nsSHistory::GloballyEvictContentViewers()
+{
+  // First, collect from each SHistory object the transactions which have a
+  // cached content viewer.  Associate with each transaction its distance from
+  // its SHistory's current index.
+
+  nsTArray<TransactionAndDistance> transactions;
+
+  PRCList* listEntry = PR_LIST_HEAD(&gSHistoryList);
+  while (listEntry != &gSHistoryList) {
+    nsSHistory* shist = static_cast<nsSHistory*>(listEntry);
+
+    // Maintain a list of the transactions which have viewers and belong to
+    // this particular shist object.  We'll add this list to the global list,
+    // |transactions|, eventually.
+    nsTArray<TransactionAndDistance> shTransactions;
+
+    // Content viewers are likely to exist only within shist->mIndex -/+
+    // gHistoryMaxViewers, so only search within that range.
+    //
+    // A content viewer might exist outside that range due to either:
+    //
+    //   * history.pushState or hash navigations, in which case a copy of the
+    //     content viewer should exist within the range, or
+    //
+    //   * bugs which cause us not to call nsSHistory::EvictContentViewers()
+    //     often enough.  Once we do call EvictContentViewers() for the
+    //     SHistory object in question, we'll do a full search of its history
+    //     and evict the out-of-range content viewers, so we don't bother here.
+    //
+    int32_t startIndex = std::max(0, shist->mIndex - gHistoryMaxViewers);
+    int32_t endIndex = std::min(shist->mLength - 1,
+                                shist->mIndex + gHistoryMaxViewers);
+    nsCOMPtr<nsISHTransaction> trans;
+    shist->GetTransactionAtIndex(startIndex, getter_AddRefs(trans));
+    for (int32_t i = startIndex; trans && i <= endIndex; i++) {
+      nsCOMPtr<nsIContentViewer> contentViewer =
+        GetContentViewerForTransaction(trans);
+
+      if (contentViewer) {
+        // Because one content viewer might belong to multiple SHEntries, we
+        // have to search through shTransactions to see if we already know
+        // about this content viewer.  If we find the viewer, update its
+        // distance from the SHistory's index and continue.
+        bool found = false;
+        for (uint32_t j = 0; j < shTransactions.Length(); j++) {
+          TransactionAndDistance& container = shTransactions[j];
+          if (container.mViewer == contentViewer) {
+            container.mDistance = std::min(container.mDistance,
+                                           DeprecatedAbs(i - shist->mIndex));
+            found = true;
+            break;
+          }
+        }
+
+        // If we didn't find a TransactionAndDistance for this content viewer,
+        // make a new one.
+        if (!found) {
+          TransactionAndDistance container(trans,
+                                           DeprecatedAbs(i - shist->mIndex));
+          shTransactions.AppendElement(container);
+        }
+      }
+
+      nsCOMPtr<nsISHTransaction> temp = trans;
+      temp->GetNext(getter_AddRefs(trans));
+    }
+
+    // We've found all the transactions belonging to shist which have viewers.
+    // Add those transactions to our global list and move on.
+    transactions.AppendElements(shTransactions);
+    listEntry = PR_NEXT_LINK(shist);
+  }
+
+  // We now have collected all cached content viewers.  First check that we
+  // have enough that we actually need to evict some.
+  if ((int32_t)transactions.Length() <= sHistoryMaxTotalViewers) {
+    return;
+  }
+
+  // If we need to evict, sort our list of transactions and evict the largest
+  // ones.  (We could of course get better algorithmic complexity here by using
+  // a heap or something more clever.  But sHistoryMaxTotalViewers isn't large,
+  // so let's not worry about it.)
+  transactions.Sort();
+
+  for (int32_t i = transactions.Length() - 1; i >= sHistoryMaxTotalViewers;
+       --i) {
+    EvictContentViewerForTransaction(transactions[i].mTransaction);
+  }
+}
+
+nsresult
+nsSHistory::EvictExpiredContentViewerForEntry(nsIBFCacheEntry* aEntry)
+{
+  int32_t startIndex = std::max(0, mIndex - gHistoryMaxViewers);
+  int32_t endIndex = std::min(mLength - 1, mIndex + gHistoryMaxViewers);
+  nsCOMPtr<nsISHTransaction> trans;
+  GetTransactionAtIndex(startIndex, getter_AddRefs(trans));
+
+  int32_t i;
+  for (i = startIndex; trans && i <= endIndex; ++i) {
+    nsCOMPtr<nsISHEntry> entry;
+    trans->GetSHEntry(getter_AddRefs(entry));
+
+    // Does entry have the same BFCacheEntry as the argument to this method?
+    if (entry->HasBFCacheEntry(aEntry)) {
+      break;
+    }
+
+    nsCOMPtr<nsISHTransaction> temp = trans;
+    temp->GetNext(getter_AddRefs(trans));
+  }
+  if (i > endIndex) {
+    return NS_OK;
+  }
+
+  if (i == mIndex) {
+    NS_WARNING("How did the current SHEntry expire?");
+    return NS_OK;
+  }
+
+  EvictContentViewerForTransaction(trans);
+
+  return NS_OK;
+}
+
+// Evicts all content viewers in all history objects.  This is very
+// inefficient, because it requires a linear search through all SHistory
+// objects for each viewer to be evicted.  However, this method is called
+// infrequently -- only when the disk or memory cache is cleared.
+
+// static
+void
+nsSHistory::GloballyEvictAllContentViewers()
+{
+  int32_t maxViewers = sHistoryMaxTotalViewers;
+  sHistoryMaxTotalViewers = 0;
+  GloballyEvictContentViewers();
+  sHistoryMaxTotalViewers = maxViewers;
+}
+
+void
+GetDynamicChildren(nsISHContainer* aContainer,
+                   nsTArray<uint64_t>& aDocshellIDs,
+                   bool aOnlyTopLevelDynamic)
+{
+  int32_t count = 0;
+  aContainer->GetChildCount(&count);
+  for (int32_t i = 0; i < count; ++i) {
+    nsCOMPtr<nsISHEntry> child;
+    aContainer->GetChildAt(i, getter_AddRefs(child));
+    if (child) {
+      bool dynAdded = false;
+      child->IsDynamicallyAdded(&dynAdded);
+      if (dynAdded) {
+        uint64_t docshellID = 0;
+        child->GetDocshellID(&docshellID);
+        aDocshellIDs.AppendElement(docshellID);
+      }
+      if (!dynAdded || !aOnlyTopLevelDynamic) {
+        nsCOMPtr<nsISHContainer> childAsContainer = do_QueryInterface(child);
+        if (childAsContainer) {
+          GetDynamicChildren(childAsContainer, aDocshellIDs,
+                             aOnlyTopLevelDynamic);
+        }
+      }
+    }
+  }
+}
+
+bool
+RemoveFromSessionHistoryContainer(nsISHContainer* aContainer,
+                                  nsTArray<uint64_t>& aDocshellIDs)
+{
+  nsCOMPtr<nsISHEntry> root = do_QueryInterface(aContainer);
+  NS_ENSURE_TRUE(root, false);
+
+  bool didRemove = false;
+  int32_t childCount = 0;
+  aContainer->GetChildCount(&childCount);
+  for (int32_t i = childCount - 1; i >= 0; --i) {
+    nsCOMPtr<nsISHEntry> child;
+    aContainer->GetChildAt(i, getter_AddRefs(child));
+    if (child) {
+      uint64_t docshelldID = 0;
+      child->GetDocshellID(&docshelldID);
+      if (aDocshellIDs.Contains(docshelldID)) {
+        didRemove = true;
+        aContainer->RemoveChild(child);
+      } else {
+        nsCOMPtr<nsISHContainer> container = do_QueryInterface(child);
+        if (container) {
+          bool childRemoved =
+            RemoveFromSessionHistoryContainer(container, aDocshellIDs);
+          if (childRemoved) {
+            didRemove = true;
+          }
+        }
+      }
+    }
+  }
+  return didRemove;
+}
+
+bool
+RemoveChildEntries(nsISHistory* aHistory, int32_t aIndex,
+                   nsTArray<uint64_t>& aEntryIDs)
+{
+  nsCOMPtr<nsISHEntry> rootHE;
+  aHistory->GetEntryAtIndex(aIndex, false, getter_AddRefs(rootHE));
+  nsCOMPtr<nsISHContainer> root = do_QueryInterface(rootHE);
+  return root ? RemoveFromSessionHistoryContainer(root, aEntryIDs) : false;
+}
+
+bool
+IsSameTree(nsISHEntry* aEntry1, nsISHEntry* aEntry2)
+{
+  if (!aEntry1 && !aEntry2) {
+    return true;
+  }
+  if ((!aEntry1 && aEntry2) || (aEntry1 && !aEntry2)) {
+    return false;
+  }
+  uint32_t id1, id2;
+  aEntry1->GetID(&id1);
+  aEntry2->GetID(&id2);
+  if (id1 != id2) {
+    return false;
+  }
+
+  nsCOMPtr<nsISHContainer> container1 = do_QueryInterface(aEntry1);
+  nsCOMPtr<nsISHContainer> container2 = do_QueryInterface(aEntry2);
+  int32_t count1, count2;
+  container1->GetChildCount(&count1);
+  container2->GetChildCount(&count2);
+  // We allow null entries in the end of the child list.
+  int32_t count = std::max(count1, count2);
+  for (int32_t i = 0; i < count; ++i) {
+    nsCOMPtr<nsISHEntry> child1, child2;
+    container1->GetChildAt(i, getter_AddRefs(child1));
+    container2->GetChildAt(i, getter_AddRefs(child2));
+    if (!IsSameTree(child1, child2)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+bool
+nsSHistory::RemoveDuplicate(int32_t aIndex, bool aKeepNext)
+{
+  NS_ASSERTION(aIndex >= 0, "aIndex must be >= 0!");
+  NS_ASSERTION(aIndex != 0 || aKeepNext,
+               "If we're removing index 0 we must be keeping the next");
+  NS_ASSERTION(aIndex != mIndex, "Shouldn't remove mIndex!");
+  int32_t compareIndex = aKeepNext ? aIndex + 1 : aIndex - 1;
+  nsCOMPtr<nsISHEntry> root1, root2;
+  GetEntryAtIndex(aIndex, false, getter_AddRefs(root1));
+  GetEntryAtIndex(compareIndex, false, getter_AddRefs(root2));
+  if (IsSameTree(root1, root2)) {
+    nsCOMPtr<nsISHTransaction> txToRemove, txToKeep, txNext, txPrev;
+    GetTransactionAtIndex(aIndex, getter_AddRefs(txToRemove));
+    GetTransactionAtIndex(compareIndex, getter_AddRefs(txToKeep));
+    if (!txToRemove) {
+      return false;
+    }
+    NS_ENSURE_TRUE(txToKeep, false);
+    txToRemove->GetNext(getter_AddRefs(txNext));
+    txToRemove->GetPrev(getter_AddRefs(txPrev));
+    txToRemove->SetNext(nullptr);
+    txToRemove->SetPrev(nullptr);
+    if (aKeepNext) {
+      if (txPrev) {
+        txPrev->SetNext(txToKeep);
+      } else {
+        txToKeep->SetPrev(nullptr);
+      }
+    } else {
+      txToKeep->SetNext(txNext);
+    }
+
+    if (aIndex == 0 && aKeepNext) {
+      NS_ASSERTION(txToRemove == mListRoot,
+                   "Transaction at index 0 should be mListRoot!");
+      // We're removing the very first session history transaction!
+      mListRoot = txToKeep;
+    }
+    if (mRootDocShell) {
+      static_cast<nsDocShell*>(mRootDocShell)->HistoryTransactionRemoved(aIndex);
+    }
+
+    // Adjust our indices to reflect the removed transaction
+    if (mIndex > aIndex) {
+      mIndex = mIndex - 1;
+    }
+
+    // NB: If the transaction we are removing is the transaction currently
+    // being navigated to (mRequestedIndex) then we adjust the index
+    // only if we're not keeping the next entry (because if we are keeping
+    // the next entry (because the current is a duplicate of the next), then
+    // that entry slides into the spot that we're currently pointing to.
+    // We don't do this adjustment for mIndex because mIndex cannot equal
+    // aIndex.
+
+    // NB: We don't need to guard on mRequestedIndex being nonzero here,
+    // because either they're strictly greater than aIndex which is at least
+    // zero, or they are equal to aIndex in which case aKeepNext must be true
+    // if aIndex is zero.
+    if (mRequestedIndex > aIndex || (mRequestedIndex == aIndex && !aKeepNext)) {
+      mRequestedIndex = mRequestedIndex - 1;
+    }
+    --mLength;
+    mEntriesInFollowingPartialHistories = 0;
+    NOTIFY_LISTENERS(OnLengthChange, (mLength));
+    return true;
+  }
+  return false;
+}
+
+NS_IMETHODIMP_(void)
+nsSHistory::RemoveEntries(nsTArray<uint64_t>& aIDs, int32_t aStartIndex)
+{
+  int32_t index = aStartIndex;
+  while (index >= 0 && RemoveChildEntries(this, --index, aIDs)) {
+  }
+  int32_t minIndex = index;
+  index = aStartIndex;
+  while (index >= 0 && RemoveChildEntries(this, index++, aIDs)) {
+  }
+
+  // We need to remove duplicate nsSHEntry trees.
+  bool didRemove = false;
+  while (index > minIndex) {
+    if (index != mIndex) {
+      didRemove = RemoveDuplicate(index, index < mIndex) || didRemove;
+    }
+    --index;
+  }
+  if (didRemove && mRootDocShell) {
+    NS_DispatchToCurrentThread(NewRunnableMethod(static_cast<nsDocShell*>(mRootDocShell),
+                                                 &nsDocShell::FireDummyOnLocationChange));
+  }
+}
+
+void
+nsSHistory::RemoveDynEntries(int32_t aOldIndex, int32_t aNewIndex)
+{
+  // Search for the entries which are in the current index,
+  // but not in the new one.
+  nsCOMPtr<nsISHEntry> originalSH;
+  GetEntryAtIndex(aOldIndex, false, getter_AddRefs(originalSH));
+  nsCOMPtr<nsISHContainer> originalContainer = do_QueryInterface(originalSH);
+  AutoTArray<uint64_t, 16> toBeRemovedEntries;
+  if (originalContainer) {
+    nsTArray<uint64_t> originalDynDocShellIDs;
+    GetDynamicChildren(originalContainer, originalDynDocShellIDs, true);
+    if (originalDynDocShellIDs.Length()) {
+      nsCOMPtr<nsISHEntry> currentSH;
+      GetEntryAtIndex(aNewIndex, false, getter_AddRefs(currentSH));
+      nsCOMPtr<nsISHContainer> newContainer = do_QueryInterface(currentSH);
+      if (newContainer) {
+        nsTArray<uint64_t> newDynDocShellIDs;
+        GetDynamicChildren(newContainer, newDynDocShellIDs, false);
+        for (uint32_t i = 0; i < originalDynDocShellIDs.Length(); ++i) {
+          if (!newDynDocShellIDs.Contains(originalDynDocShellIDs[i])) {
+            toBeRemovedEntries.AppendElement(originalDynDocShellIDs[i]);
+          }
+        }
+      }
+    }
+  }
+  if (toBeRemovedEntries.Length()) {
+    RemoveEntries(toBeRemovedEntries, aOldIndex);
+  }
+}
+
+NS_IMETHODIMP
+nsSHistory::UpdateIndex()
+{
+  // Update the actual index with the right value.
+  if (mIndex != mRequestedIndex && mRequestedIndex != -1) {
+    RemoveDynEntries(mIndex, mRequestedIndex);
+    mIndex = mRequestedIndex;
+  }
+
+  mRequestedIndex = -1;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::Stop(uint32_t aStopFlags)
+{
+  // Not implemented
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::GetDocument(nsIDOMDocument** aDocument)
+{
+  // Not implemented
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::GetCurrentURI(nsIURI** aResultURI)
+{
+  NS_ENSURE_ARG_POINTER(aResultURI);
+  nsresult rv;
+
+  nsCOMPtr<nsISHEntry> currentEntry;
+  rv = GetEntryAtIndex(mIndex, false, getter_AddRefs(currentEntry));
+  if (NS_FAILED(rv) && !currentEntry) {
+    return rv;
+  }
+  rv = currentEntry->GetURI(aResultURI);
+  return rv;
+}
+
+NS_IMETHODIMP
+nsSHistory::GetReferringURI(nsIURI** aURI)
+{
+  *aURI = nullptr;
+  // Not implemented
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::SetSessionHistory(nsISHistory* aSessionHistory)
+{
+  // Not implemented
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::GetSessionHistory(nsISHistory** aSessionHistory)
+{
+  // Not implemented
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::LoadURIWithOptions(const char16_t* aURI,
+                               uint32_t aLoadFlags,
+                               nsIURI* aReferringURI,
+                               uint32_t aReferrerPolicy,
+                               nsIInputStream* aPostStream,
+                               nsIInputStream* aExtraHeaderStream,
+                               nsIURI* aBaseURI)
+{
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::SetOriginAttributesBeforeLoading(JS::HandleValue aOriginAttributes)
+{
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::LoadURI(const char16_t* aURI,
+                    uint32_t aLoadFlags,
+                    nsIURI* aReferringURI,
+                    nsIInputStream* aPostStream,
+                    nsIInputStream* aExtraHeaderStream)
+{
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::GotoIndex(int32_t aGlobalIndex)
+{
+  // We provide abstraction of grouped session history for nsIWebNavigation
+  // functions, so the index passed in here is global index.
+  return LoadEntry(aGlobalIndex - mGlobalIndexOffset, nsIDocShellLoadInfo::loadHistory,
+                   HIST_CMD_GOTOINDEX);
+}
+
+nsresult
+nsSHistory::LoadNextPossibleEntry(int32_t aNewIndex, long aLoadType,
+                                  uint32_t aHistCmd)
+{
+  mRequestedIndex = -1;
+  if (aNewIndex < mIndex) {
+    return LoadEntry(aNewIndex - 1, aLoadType, aHistCmd);
+  }
+  if (aNewIndex > mIndex) {
+    return LoadEntry(aNewIndex + 1, aLoadType, aHistCmd);
+  }
+  return NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsSHistory::LoadEntry(int32_t aIndex, long aLoadType, uint32_t aHistCmd)
+{
+  if (!mRootDocShell) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (aIndex < 0 || aIndex >= mLength) {
+    if (aIndex + mGlobalIndexOffset < 0) {
+      // The global index is negative.
+      return NS_ERROR_FAILURE;
+    }
+
+    if (aIndex - mLength >= mEntriesInFollowingPartialHistories) {
+      // The global index exceeds max possible value.
+      return NS_ERROR_FAILURE;
+    }
+
+    // The global index is valid. trigger cross browser navigation.
+    nsCOMPtr<nsIPartialSHistoryListener> listener =
+      do_QueryReferent(mPartialHistoryListener);
+    if (!listener) {
+      return NS_ERROR_FAILURE;
+    }
+    return listener->OnRequestCrossBrowserNavigation(aIndex + mGlobalIndexOffset);
+  }
+
+  // Keep note of requested history index in mRequestedIndex.
+  mRequestedIndex = aIndex;
+
+  nsCOMPtr<nsISHEntry> prevEntry;
+  GetEntryAtIndex(mIndex, false, getter_AddRefs(prevEntry));
+
+  nsCOMPtr<nsISHEntry> nextEntry;
+  GetEntryAtIndex(mRequestedIndex, false, getter_AddRefs(nextEntry));
+  if (!nextEntry || !prevEntry) {
+    mRequestedIndex = -1;
+    return NS_ERROR_FAILURE;
+  }
+
+  // Remember that this entry is getting loaded at this point in the sequence
+  nsCOMPtr<nsISHEntryInternal> entryInternal = do_QueryInterface(nextEntry);
+
+  if (entryInternal) {
+    entryInternal->SetLastTouched(++gTouchCounter);
+  }
+
+  // Send appropriate listener notifications
+  bool canNavigate = true;
+  // Get the uri for the entry we are about to visit
+  nsCOMPtr<nsIURI> nextURI;
+  nextEntry->GetURI(getter_AddRefs(nextURI));
+
+  if (aHistCmd == HIST_CMD_BACK) {
+    // We are going back one entry. Send GoBack notifications
+    NOTIFY_LISTENERS_CANCELABLE(OnHistoryGoBack, canNavigate,
+                                (nextURI, &canNavigate));
+  } else if (aHistCmd == HIST_CMD_FORWARD) {
+    // We are going forward. Send GoForward notification
+    NOTIFY_LISTENERS_CANCELABLE(OnHistoryGoForward, canNavigate,
+                                (nextURI, &canNavigate));
+  } else if (aHistCmd == HIST_CMD_GOTOINDEX) {
+    // We are going somewhere else. This is not reload either
+    NOTIFY_LISTENERS_CANCELABLE(OnHistoryGotoIndex, canNavigate,
+                                (aIndex, nextURI, &canNavigate));
+  }
+
+  if (!canNavigate) {
+    // If the listener asked us not to proceed with
+    // the operation, simply return.
+    mRequestedIndex = -1;
+    return NS_OK;  // XXX Maybe I can return some other error code?
+  }
+
+  if (mRequestedIndex == mIndex) {
+    // Possibly a reload case
+    return InitiateLoad(nextEntry, mRootDocShell, aLoadType);
+  }
+
+  // Going back or forward.
+  bool differenceFound = false;
+  nsresult rv = LoadDifferingEntries(prevEntry, nextEntry, mRootDocShell,
+                                     aLoadType, differenceFound);
+  if (!differenceFound) {
+    // We did not find any differences. Go further in the history.
+    return LoadNextPossibleEntry(aIndex, aLoadType, aHistCmd);
+  }
+
+  return rv;
+}
+
+nsresult
+nsSHistory::LoadDifferingEntries(nsISHEntry* aPrevEntry, nsISHEntry* aNextEntry,
+                                 nsIDocShell* aParent, long aLoadType,
+                                 bool& aDifferenceFound)
+{
+  if (!aPrevEntry || !aNextEntry || !aParent) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsresult result = NS_OK;
+  uint32_t prevID, nextID;
+
+  aPrevEntry->GetID(&prevID);
+  aNextEntry->GetID(&nextID);
+
+  // Check the IDs to verify if the pages are different.
+  if (prevID != nextID) {
+    aDifferenceFound = true;
+
+    // Set the Subframe flag if not navigating the root docshell.
+    aNextEntry->SetIsSubFrame(aParent != mRootDocShell);
+    return InitiateLoad(aNextEntry, aParent, aLoadType);
+  }
+
+  // The entries are the same, so compare any child frames
+  int32_t pcnt = 0;
+  int32_t ncnt = 0;
+  int32_t dsCount = 0;
+  nsCOMPtr<nsISHContainer> prevContainer(do_QueryInterface(aPrevEntry));
+  nsCOMPtr<nsISHContainer> nextContainer(do_QueryInterface(aNextEntry));
+
+  if (!prevContainer || !nextContainer) {
+    return NS_ERROR_FAILURE;
+  }
+
+  prevContainer->GetChildCount(&pcnt);
+  nextContainer->GetChildCount(&ncnt);
+  aParent->GetChildCount(&dsCount);
+
+  // Create an array for child docshells.
+  nsCOMArray<nsIDocShell> docshells;
+  for (int32_t i = 0; i < dsCount; ++i) {
+    nsCOMPtr<nsIDocShellTreeItem> treeItem;
+    aParent->GetChildAt(i, getter_AddRefs(treeItem));
+    nsCOMPtr<nsIDocShell> shell = do_QueryInterface(treeItem);
+    if (shell) {
+      docshells.AppendElement(shell.forget());
+    }
+  }
+
+  // Search for something to load next.
+  for (int32_t i = 0; i < ncnt; ++i) {
+    // First get an entry which may cause a new page to be loaded.
+    nsCOMPtr<nsISHEntry> nChild;
+    nextContainer->GetChildAt(i, getter_AddRefs(nChild));
+    if (!nChild) {
+      continue;
+    }
+    uint64_t docshellID = 0;
+    nChild->GetDocshellID(&docshellID);
+
+    // Then find the associated docshell.
+    nsIDocShell* dsChild = nullptr;
+    int32_t count = docshells.Count();
+    for (int32_t j = 0; j < count; ++j) {
+      uint64_t shellID = 0;
+      nsIDocShell* shell = docshells[j];
+      shell->GetHistoryID(&shellID);
+      if (shellID == docshellID) {
+        dsChild = shell;
+        break;
+      }
+    }
+    if (!dsChild) {
+      continue;
+    }
+
+    // Then look at the previous entries to see if there was
+    // an entry for the docshell.
+    nsCOMPtr<nsISHEntry> pChild;
+    for (int32_t k = 0; k < pcnt; ++k) {
+      nsCOMPtr<nsISHEntry> child;
+      prevContainer->GetChildAt(k, getter_AddRefs(child));
+      if (child) {
+        uint64_t dID = 0;
+        child->GetDocshellID(&dID);
+        if (dID == docshellID) {
+          pChild = child;
+          break;
+        }
+      }
+    }
+
+    // Finally recursively call this method.
+    // This will either load a new page to shell or some subshell or
+    // do nothing.
+    LoadDifferingEntries(pChild, nChild, dsChild, aLoadType, aDifferenceFound);
+  }
+  return result;
+}
+
+nsresult
+nsSHistory::InitiateLoad(nsISHEntry* aFrameEntry, nsIDocShell* aFrameDS,
+                         long aLoadType)
+{
+  NS_ENSURE_STATE(aFrameDS && aFrameEntry);
+
+  nsCOMPtr<nsIDocShellLoadInfo> loadInfo;
+
+  /* Set the loadType in the SHEntry too to  what was passed on.
+   * This will be passed on to child subframes later in nsDocShell,
+   * so that proper loadType is maintained through out a frameset
+   */
+  aFrameEntry->SetLoadType(aLoadType);
+  aFrameDS->CreateLoadInfo(getter_AddRefs(loadInfo));
+
+  loadInfo->SetLoadType(aLoadType);
+  loadInfo->SetSHEntry(aFrameEntry);
+
+  nsCOMPtr<nsIURI> originalURI;
+  aFrameEntry->GetOriginalURI(getter_AddRefs(originalURI));
+  loadInfo->SetOriginalURI(originalURI);
+
+  bool loadReplace;
+  aFrameEntry->GetLoadReplace(&loadReplace);
+  loadInfo->SetLoadReplace(loadReplace);
+
+  nsCOMPtr<nsIURI> nextURI;
+  aFrameEntry->GetURI(getter_AddRefs(nextURI));
+  // Time   to initiate a document load
+  return aFrameDS->LoadURI(nextURI, loadInfo,
+                           nsIWebNavigation::LOAD_FLAGS_NONE, false);
+
+}
+
+NS_IMETHODIMP
+nsSHistory::SetRootDocShell(nsIDocShell* aDocShell)
+{
+  mRootDocShell = aDocShell;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::GetSHistoryEnumerator(nsISimpleEnumerator** aEnumerator)
+{
+  NS_ENSURE_ARG_POINTER(aEnumerator);
+  RefPtr<nsSHEnumerator> iterator = new nsSHEnumerator(this);
+  iterator.forget(aEnumerator);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHistory::OnAttachGroupedSessionHistory(int32_t aOffset)
+{
+  NS_ENSURE_TRUE(!mIsPartial, NS_ERROR_UNEXPECTED);
+  NS_ENSURE_TRUE(aOffset >= 0, NS_ERROR_ILLEGAL_VALUE);
+
+  mIsPartial = true;
+  mGlobalIndexOffset = aOffset;
+
+  // The last attached history is always at the end of the group.
+  mEntriesInFollowingPartialHistories = 0;
+
+  // Setting grouped history info may change canGoBack / canGoForward.
+  // Send a location change to update these values.
+  NS_DispatchToCurrentThread(NewRunnableMethod(static_cast<nsDocShell*>(mRootDocShell),
+                                               &nsDocShell::FireDummyOnLocationChange));
+  return NS_OK;
+
+}
+
+nsSHEnumerator::nsSHEnumerator(nsSHistory* aSHistory) : mIndex(-1)
+{
+  mSHistory = aSHistory;
+}
+
+nsSHEnumerator::~nsSHEnumerator()
+{
+  mSHistory = nullptr;
+}
+
+NS_IMPL_ISUPPORTS(nsSHEnumerator, nsISimpleEnumerator)
+
+NS_IMETHODIMP
+nsSHEnumerator::HasMoreElements(bool* aReturn)
+{
+  int32_t cnt;
+  *aReturn = false;
+  mSHistory->GetCount(&cnt);
+  if (mIndex >= -1 && mIndex < (cnt - 1)) {
+    *aReturn = true;
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHEnumerator::GetNext(nsISupports** aItem)
+{
+  NS_ENSURE_ARG_POINTER(aItem);
+  int32_t cnt = 0;
+
+  nsresult result = NS_ERROR_FAILURE;
+  mSHistory->GetCount(&cnt);
+  if (mIndex < (cnt - 1)) {
+    mIndex++;
+    nsCOMPtr<nsISHEntry> hEntry;
+    result = mSHistory->GetEntryAtIndex(mIndex, false, getter_AddRefs(hEntry));
+    if (hEntry) {
+      result = CallQueryInterface(hEntry, aItem);
+    }
+  }
+  return result;
+}