From 8beb65dd501cbdcfd6a793027b5de2a1fdfc7149 Mon Sep 17 00:00:00 2001
From: "Matt A. Tobin" <email@mattatobin.com>
Date: Fri, 17 Apr 2020 07:08:22 -0400
Subject: Bug 1418002 - Remove HTMLContentElement

Tag #1375
---
 dom/base/ChildIterator.cpp                         |  21 +-
 dom/base/ShadowRoot.cpp                            | 266 +--------------
 dom/base/ShadowRoot.h                              |  36 --
 dom/base/nsContentUtils.cpp                        |  14 +-
 dom/html/HTMLContentElement.cpp                    | 379 ---------------------
 dom/html/HTMLContentElement.h                      | 126 -------
 dom/html/moz.build                                 |   2 -
 dom/tests/mochitest/webcomponents/mochitest.ini    |   4 -
 .../webcomponents/test_dest_insertion_points.html  |  73 ----
 .../test_dynamic_content_element_matching.html     |  50 ---
 .../test_fallback_dest_insertion_points.html       |  71 ----
 .../webcomponents/test_nested_content_element.html | 127 -------
 dom/webidl/HTMLContentElement.webidl               |  20 --
 dom/webidl/moz.build                               |   1 -
 14 files changed, 12 insertions(+), 1178 deletions(-)
 delete mode 100644 dom/html/HTMLContentElement.cpp
 delete mode 100644 dom/html/HTMLContentElement.h
 delete mode 100644 dom/tests/mochitest/webcomponents/test_dest_insertion_points.html
 delete mode 100644 dom/tests/mochitest/webcomponents/test_dynamic_content_element_matching.html
 delete mode 100644 dom/tests/mochitest/webcomponents/test_fallback_dest_insertion_points.html
 delete mode 100644 dom/tests/mochitest/webcomponents/test_nested_content_element.html
 delete mode 100644 dom/webidl/HTMLContentElement.webidl

(limited to 'dom')

diff --git a/dom/base/ChildIterator.cpp b/dom/base/ChildIterator.cpp
index 391b7c326..dc356fc01 100644
--- a/dom/base/ChildIterator.cpp
+++ b/dom/base/ChildIterator.cpp
@@ -7,7 +7,6 @@
 #include "ChildIterator.h"
 #include "nsContentUtils.h"
 #include "mozilla/dom/XBLChildrenElement.h"
-#include "mozilla/dom/HTMLContentElement.h"
 #include "mozilla/dom/ShadowRoot.h"
 #include "nsIAnonymousContentCreator.h"
 #include "nsIFrame.h"
@@ -18,33 +17,29 @@ namespace dom {
 
 class MatchedNodes {
 public:
-  explicit MatchedNodes(HTMLContentElement* aInsertionPoint)
-    : mIsContentElement(true), mContentElement(aInsertionPoint) {}
-
+  explicit MatchedNodes()
+    : mIsContentElement(false), mChildrenElement(nullptr) {}
   explicit MatchedNodes(XBLChildrenElement* aInsertionPoint)
     : mIsContentElement(false), mChildrenElement(aInsertionPoint) {}
 
   uint32_t Length() const
   {
-    return mIsContentElement ? mContentElement->MatchedNodes().Length()
-                             : mChildrenElement->InsertedChildrenLength();
+    return mChildrenElement ? mChildrenElement->InsertedChildrenLength() : 0;
   }
 
   nsIContent* operator[](int32_t aIndex) const
   {
-    return mIsContentElement ? mContentElement->MatchedNodes()[aIndex]
-                             : mChildrenElement->InsertedChild(aIndex);
+    return mChildrenElement ? mChildrenElement->InsertedChild(aIndex) : nullptr;
   }
 
   bool IsEmpty() const
   {
-    return mIsContentElement ? mContentElement->MatchedNodes().IsEmpty()
-                             : !mChildrenElement->HasInsertedChildren();
+    return mChildrenElement && !mChildrenElement->HasInsertedChildren();
   }
 protected:
+  // Leftover from Shadow DOM v0.
   bool mIsContentElement;
   union {
-    HTMLContentElement* mContentElement;
     XBLChildrenElement* mChildrenElement;
   };
 };
@@ -57,9 +52,9 @@ GetMatchedNodesForPoint(nsIContent* aContent)
     return MatchedNodes(static_cast<XBLChildrenElement*>(aContent));
   }
 
+  return MatchedNodes();
   // Web components case
-  MOZ_ASSERT(aContent->IsHTMLElement(nsGkAtoms::content));
-  return MatchedNodes(HTMLContentElement::FromContent(aContent));
+  // XXX handle <slot> element?
 }
 
 nsIContent*
diff --git a/dom/base/ShadowRoot.cpp b/dom/base/ShadowRoot.cpp
index e00bb69d8..97214e050 100644
--- a/dom/base/ShadowRoot.cpp
+++ b/dom/base/ShadowRoot.cpp
@@ -14,7 +14,6 @@
 #include "nsIDOMHTMLElement.h"
 #include "nsIStyleSheetLinkingElement.h"
 #include "mozilla/dom/Element.h"
-#include "mozilla/dom/HTMLContentElement.h"
 #include "nsXBLPrototypeBinding.h"
 #include "mozilla/StyleSheet.h"
 #include "mozilla/StyleSheetInlines.h"
@@ -223,35 +222,6 @@ ShadowRoot::GetElementsByClassName(const nsAString& aClasses)
   return nsContentUtils::GetElementsByClassName(this, aClasses);
 }
 
-void
-ShadowRoot::AddInsertionPoint(HTMLContentElement* aInsertionPoint)
-{
-  TreeOrderComparator comparator;
-  mInsertionPoints.InsertElementSorted(aInsertionPoint, comparator);
-}
-
-void
-ShadowRoot::RemoveInsertionPoint(HTMLContentElement* aInsertionPoint)
-{
-  mInsertionPoints.RemoveElement(aInsertionPoint);
-}
-
-void
-ShadowRoot::RemoveDestInsertionPoint(nsIContent* aInsertionPoint,
-                                     nsTArray<nsIContent*>& aDestInsertionPoints)
-{
-  // Remove the insertion point from the destination insertion points.
-  // Also remove all succeeding insertion points because it is no longer
-  // possible for the content to be distributed into deeper node trees.
-  int32_t index = aDestInsertionPoints.IndexOf(aInsertionPoint);
-
-  // It's possible that we already removed the insertion point while processing
-  // other insertion point removals.
-  if (index >= 0) {
-    aDestInsertionPoints.SetLength(index);
-  }
-}
-
 void
 ShadowRoot::DistributionChanged()
 {
@@ -269,133 +239,10 @@ ShadowRoot::DistributionChanged()
   shell->DestroyFramesForAndRestyle(host);
 }
 
-const HTMLContentElement*
-ShadowRoot::DistributeSingleNode(nsIContent* aContent)
-{
-  // Find the insertion point to which the content belongs.
-  HTMLContentElement* foundInsertionPoint = nullptr;
-  for (HTMLContentElement* insertionPoint : mInsertionPoints) {
-    if (insertionPoint->Match(aContent)) {
-      if (insertionPoint->MatchedNodes().Contains(aContent)) {
-        // Node is already matched into the insertion point. We are done.
-        return insertionPoint;
-      }
-
-      // Matching may cause the insertion point to drop fallback content.
-      if (insertionPoint->MatchedNodes().IsEmpty() &&
-          insertionPoint->HasChildren()) {
-        // This match will cause the insertion point to drop all fallback
-        // content and used matched nodes instead. Give up on the optimization
-        // and just distribute all nodes.
-        DistributeAllNodes();
-        MOZ_ASSERT(insertionPoint->MatchedNodes().Contains(aContent));
-        return insertionPoint;
-      }
-      foundInsertionPoint = insertionPoint;
-      break;
-    }
-  }
-
-  if (!foundInsertionPoint) {
-    return nullptr;
-  }
-
-  // Find the index into the insertion point.
-  nsCOMArray<nsIContent>& matchedNodes = foundInsertionPoint->MatchedNodes();
-  // Find the appropriate position in the matched node list for the
-  // newly distributed content.
-  bool isIndexFound = false;
-  ExplicitChildIterator childIterator(GetHost());
-  for (uint32_t i = 0; i < matchedNodes.Length(); i++) {
-    // Seek through the host's explicit children until the inserted content
-    // is found or when the current matched node is reached.
-    if (childIterator.Seek(aContent, matchedNodes[i])) {
-      // aContent was found before the current matched node.
-      foundInsertionPoint->InsertMatchedNode(i, aContent);
-      isIndexFound = true;
-      break;
-    }
-  }
-
-  if (!isIndexFound) {
-    // We have still not found an index in the insertion point,
-    // thus it must be at the end.
-    MOZ_ASSERT(childIterator.Seek(aContent, nullptr),
-               "Trying to match a node that is not a candidate to be matched");
-    foundInsertionPoint->AppendMatchedNode(aContent);
-  }
-
-  return foundInsertionPoint;
-}
-
-const HTMLContentElement*
-ShadowRoot::RemoveDistributedNode(nsIContent* aContent)
-{
-  // Find insertion point containing the content and remove the node.
-  for (HTMLContentElement* insertionPoint : mInsertionPoints) {
-    if (!insertionPoint->MatchedNodes().Contains(aContent)) {
-      continue;
-    }
-
-    // Removing the matched node may cause the insertion point to use
-    // fallback content.
-    if (insertionPoint->MatchedNodes().Length() == 1 &&
-        insertionPoint->HasChildren()) {
-      // Removing the matched node will cause fallback content to be
-      // used instead. Give up optimization and distribute all nodes.
-      DistributeAllNodes();
-      return insertionPoint;
-    }
-
-    insertionPoint->RemoveMatchedNode(aContent);
-    return insertionPoint;
-  }
-
-  return nullptr;
-}
-
 void
 ShadowRoot::DistributeAllNodes()
 {
-  // Create node pool.
-  nsTArray<nsIContent*> nodePool;
-  ExplicitChildIterator childIterator(GetHost());
-  for (nsIContent* content = childIterator.GetNextChild(); content;
-       content = childIterator.GetNextChild()) {
-    nodePool.AppendElement(content);
-  }
-
-  nsTArray<ShadowRoot*> shadowsToUpdate;
-
-  for (HTMLContentElement* insertionPoint : mInsertionPoints) {
-    insertionPoint->ClearMatchedNodes();
-    // Assign matching nodes from node pool.
-    for (uint32_t j = 0; j < nodePool.Length(); j++) {
-      if (insertionPoint->Match(nodePool[j])) {
-        insertionPoint->AppendMatchedNode(nodePool[j]);
-        nodePool.RemoveElementAt(j--);
-      }
-    }
-
-    // Keep track of instances where the content insertion point is distributed
-    // (parent of insertion point has a ShadowRoot).
-    nsIContent* insertionParent = insertionPoint->GetParent();
-    MOZ_ASSERT(insertionParent, "The only way for an insertion point to be in the"
-                                "mInsertionPoints array is to be a descendant of a"
-                                "ShadowRoot, in which case, it should have a parent");
-
-    // If the parent of the insertion point has a ShadowRoot, the nodes distributed
-    // to the insertion point must be reprojected to the insertion points of the
-    // parent's ShadowRoot.
-    ShadowRoot* parentShadow = insertionParent->GetShadowRoot();
-    if (parentShadow && !shadowsToUpdate.Contains(parentShadow)) {
-      shadowsToUpdate.AppendElement(parentShadow);
-    }
-  }
-
-  for (ShadowRoot* shadow : shadowsToUpdate) {
-    shadow->DistributeAllNodes();
-  }
+  //XXX Handle <slot>.
 
   DistributionChanged();
 }
@@ -475,13 +322,6 @@ ShadowRoot::IsPooledNode(nsIContent* aContent) const
     return true;
   }
 
-  if (auto* content = HTMLContentElement::FromContentOrNull(container)) {
-    // Fallback content will end up in pool if its parent is a child of the host.
-    return content->IsInsertionPoint() &&
-           content->MatchedNodes().IsEmpty() &&
-           container->GetParentNode() == host;
-  }
-
   return false;
 }
 
@@ -497,13 +337,6 @@ ShadowRoot::AttributeChanged(nsIDocument* aDocument,
     return;
   }
 
-  // Attributes may change insertion point matching, find its new distribution.
-  //
-  // FIXME(emilio): What about state changes?
-  if (!RedistributeElement(aElement)) {
-    return;
-  }
-
   if (!aElement->IsInComposedDoc()) {
     return;
   }
@@ -513,52 +346,10 @@ ShadowRoot::AttributeChanged(nsIDocument* aDocument,
     return;
   }
 
+  //XXX optimize this!
   shell->DestroyFramesForAndRestyle(aElement);
 }
 
-bool
-ShadowRoot::RedistributeElement(Element* aElement)
-{
-  auto* oldInsertionPoint = RemoveDistributedNode(aElement);
-  auto* newInsertionPoint = DistributeSingleNode(aElement);
-
-  if (oldInsertionPoint == newInsertionPoint) {
-    if (oldInsertionPoint) {
-      if (auto* shadow = oldInsertionPoint->GetParent()->GetShadowRoot()) {
-        return shadow->RedistributeElement(aElement);
-      }
-    }
-
-    return false;
-  }
-
-  while (oldInsertionPoint) {
-    // Handle the case where the parent of the insertion point has a ShadowRoot.
-    // The node distributed into the insertion point must be reprojected to the
-    // insertion points of the parent's ShadowRoot.
-    auto* shadow = oldInsertionPoint->GetParent()->GetShadowRoot();
-    if (!shadow) {
-      break;
-    }
-
-    oldInsertionPoint = shadow->RemoveDistributedNode(aElement);
-  }
-
-  while (newInsertionPoint) {
-    // Handle the case where the parent of the insertion point has a ShadowRoot.
-    // The node distributed into the insertion point must be reprojected to the
-    // insertion points of the parent's ShadowRoot.
-    auto* shadow = newInsertionPoint->GetParent()->GetShadowRoot();
-    if (!shadow) {
-      break;
-    }
-
-    newInsertionPoint = shadow->DistributeSingleNode(aElement);
-  }
-
-  return true;
-}
-
 void
 ShadowRoot::ContentAppended(nsIDocument* aDocument,
                             nsIContent* aContainer,
@@ -583,31 +374,6 @@ ShadowRoot::ContentInserted(nsIDocument* aDocument,
     mInsertionPointChanged = false;
     return;
   }
-
-  // Add insertion point to destination insertion points of fallback content.
-  if (nsContentUtils::IsContentInsertionPoint(aContainer)) {
-    HTMLContentElement* content = HTMLContentElement::FromContent(aContainer);
-    if (content && content->MatchedNodes().IsEmpty()) {
-      aChild->DestInsertionPoints().AppendElement(aContainer);
-    }
-  }
-
-  // Watch for new nodes added to the pool because the node
-  // may need to be added to an insertion point.
-  if (IsPooledNode(aChild)) {
-    auto* insertionPoint = DistributeSingleNode(aChild);
-    while (insertionPoint) {
-      // Handle the case where the parent of the insertion point has a ShadowRoot.
-      // The node distributed into the insertion point must be reprojected to the
-      // insertion points of the parent's ShadowRoot.
-      auto* parentShadow = insertionPoint->GetParent()->GetShadowRoot();
-      if (!parentShadow) {
-        break;
-      }
-
-      insertionPoint = parentShadow->DistributeSingleNode(aChild);
-    }
-  }
 }
 
 void
@@ -622,34 +388,6 @@ ShadowRoot::ContentRemoved(nsIDocument* aDocument,
     mInsertionPointChanged = false;
     return;
   }
-
-  // Clear destination insertion points for removed
-  // fallback content.
-  if (nsContentUtils::IsContentInsertionPoint(aContainer)) {
-    HTMLContentElement* content = HTMLContentElement::FromContent(aContainer);
-    if (content->MatchedNodes().IsEmpty()) {
-      aChild->DestInsertionPoints().Clear();
-    }
-  }
-
-  // Watch for node that is removed from the pool because
-  // it may need to be removed from an insertion point.
-  if (IsPooledNode(aChild)) {
-    auto* insertionPoint = RemoveDistributedNode(aChild);
-    while (insertionPoint) {
-      // Handle the case where the parent of the insertion point has a
-      // ShadowRoot.
-      //
-      // The removed node needs to be removed from the insertion points of the
-      // parent's ShadowRoot.
-      auto* parentShadow = insertionPoint->GetParent()->GetShadowRoot();
-      if (!parentShadow) {
-        break;
-      }
-
-      insertionPoint = parentShadow->RemoveDistributedNode(aChild);
-    }
-  }
 }
 
 nsresult
diff --git a/dom/base/ShadowRoot.h b/dom/base/ShadowRoot.h
index 4a5b54e85..5efff5be7 100644
--- a/dom/base/ShadowRoot.h
+++ b/dom/base/ShadowRoot.h
@@ -24,7 +24,6 @@ namespace mozilla {
 namespace dom {
 
 class Element;
-class HTMLContentElement;
 class ShadowRootStyleSheetList;
 
 class ShadowRoot final : public DocumentFragment,
@@ -73,28 +72,6 @@ public:
   void DistributeAllNodes();
 
 private:
-  /**
-   * Distributes a single explicit child of the pool host to the content
-   * insertion points in this ShadowRoot.
-   *
-   * Returns the insertion point the element is distributed to after this call.
-   *
-   * Note that this doesn't handle distributing the node in the insertion point
-   * parent's shadow root.
-   */
-  const HTMLContentElement* DistributeSingleNode(nsIContent* aContent);
-
-  /**
-   * Removes a single explicit child of the pool host from the content
-   * insertion points in this ShadowRoot.
-   *
-   * Returns the old insertion point, if any.
-   *
-   * Note that this doesn't handle removing the node in the returned insertion
-   * point parent's shadow root.
-   */
-  const HTMLContentElement* RemoveDistributedNode(nsIContent* aContent);
-
   /**
    * Redistributes a node of the pool, and returns whether the distribution
    * changed.
@@ -109,9 +86,6 @@ private:
   bool IsPooledNode(nsIContent* aChild) const;
 
 public:
-  void AddInsertionPoint(HTMLContentElement* aInsertionPoint);
-  void RemoveInsertionPoint(HTMLContentElement* aInsertionPoint);
-
   void SetInsertionPointChanged() { mInsertionPointChanged = true; }
 
   void SetAssociatedBinding(nsXBLBinding* aBinding) { mAssociatedBinding = aBinding; }
@@ -120,9 +94,6 @@ public:
 
   static ShadowRoot* FromNode(nsINode* aNode);
 
-  static void RemoveDestInsertionPoint(nsIContent* aInsertionPoint,
-                                       nsTArray<nsIContent*>& aDestInsertionPoints);
-
   // WebIDL methods.
   Element* GetElementById(const nsAString& aElementId);
   already_AddRefed<nsContentList>
@@ -147,13 +118,6 @@ protected:
 
   ShadowRootMode mMode;
 
-  // An array of content insertion points that are a descendant of the ShadowRoot
-  // sorted in tree order. Insertion points are responsible for notifying
-  // the ShadowRoot when they are removed or added as a descendant. The insertion
-  // points are kept alive by the parent node, thus weak references are held
-  // by the array.
-  nsTArray<HTMLContentElement*> mInsertionPoints;
-
   nsTHashtable<nsIdentifierMapEntry> mIdentifierMap;
   nsXBLPrototypeBinding* mProtoBinding;
 
diff --git a/dom/base/nsContentUtils.cpp b/dom/base/nsContentUtils.cpp
index 3d23bedea..038da24b4 100644
--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -45,7 +45,6 @@
 #include "mozilla/dom/FileSystemSecurity.h"
 #include "mozilla/dom/HTMLMediaElement.h"
 #include "mozilla/dom/HTMLTemplateElement.h"
-#include "mozilla/dom/HTMLContentElement.h"
 #include "mozilla/dom/ipc/BlobChild.h"
 #include "mozilla/dom/ipc/BlobParent.h"
 #include "mozilla/dom/Promise.h"
@@ -7036,9 +7035,8 @@ nsContentUtils::IsContentInsertionPoint(nsIContent* aContent)
   }
 
   // Check if the content is a web components content insertion point.
-  HTMLContentElement* contentElement =
-    HTMLContentElement::FromContent(aContent);
-  return contentElement && contentElement->IsInsertionPoint();
+  // XXX handle <slot>?
+  return false;
 }
 
 // static
@@ -7055,14 +7053,6 @@ nsContentUtils::HasDistributedChildren(nsIContent* aContent)
     return true;
   }
 
-  HTMLContentElement* contentEl = HTMLContentElement::FromContent(aContent);
-  if (contentEl && contentEl->IsInsertionPoint()) {
-    // Children of a content insertion point are distributed to the
-    // content insertion point if the content insertion point does
-    // not match any nodes (fallback content).
-    return contentEl->MatchedNodes().IsEmpty();
-  }
-
   return false;
 }
 
diff --git a/dom/html/HTMLContentElement.cpp b/dom/html/HTMLContentElement.cpp
deleted file mode 100644
index 15d79c761..000000000
--- a/dom/html/HTMLContentElement.cpp
+++ /dev/null
@@ -1,379 +0,0 @@
-/* -*- 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 "mozilla/dom/HTMLContentElement.h"
-#include "mozilla/dom/HTMLContentElementBinding.h"
-#include "mozilla/dom/HTMLUnknownElement.h"
-#include "mozilla/dom/NodeListBinding.h"
-#include "mozilla/dom/ShadowRoot.h"
-#include "mozilla/css/StyleRule.h"
-#include "nsGkAtoms.h"
-#include "nsStyleConsts.h"
-#include "nsIAtom.h"
-#include "nsCSSRuleProcessor.h"
-#include "nsRuleData.h"
-#include "nsRuleProcessorData.h"
-#include "nsRuleWalker.h"
-#include "nsCSSParser.h"
-#include "nsDocument.h"
-
-// Expand NS_IMPL_NS_NEW_HTML_ELEMENT(Content) to add check for web components
-// being enabled.
-nsGenericHTMLElement*
-NS_NewHTMLContentElement(already_AddRefed<mozilla::dom::NodeInfo>&& aNodeInfo,
-                         mozilla::dom::FromParser aFromParser)
-{
-  // When this check is removed, remove the nsDocument.h and
-  // HTMLUnknownElement.h includes.  Also remove nsINode::IsHTMLContentElement.
-  //
-  // We have to jump through some hoops to be able to produce both NodeInfo* and
-  // already_AddRefed<NodeInfo>& for our callees.
-  RefPtr<mozilla::dom::NodeInfo> nodeInfo(aNodeInfo);
-  if (!nsDocument::IsWebComponentsEnabled(nodeInfo)) {
-    already_AddRefed<mozilla::dom::NodeInfo> nodeInfoArg(nodeInfo.forget());
-    return new mozilla::dom::HTMLUnknownElement(nodeInfoArg);
-  }
-
-  already_AddRefed<mozilla::dom::NodeInfo> nodeInfoArg(nodeInfo.forget());
-  return new mozilla::dom::HTMLContentElement(nodeInfoArg);
-}
-
-using namespace mozilla::dom;
-
-HTMLContentElement::HTMLContentElement(already_AddRefed<mozilla::dom::NodeInfo>& aNodeInfo)
-  : nsGenericHTMLElement(aNodeInfo), mValidSelector(true), mIsInsertionPoint(false)
-{
-}
-
-HTMLContentElement::~HTMLContentElement()
-{
-}
-
-NS_IMPL_CYCLE_COLLECTION_INHERITED(HTMLContentElement,
-                                   nsGenericHTMLElement,
-                                   mMatchedNodes)
-
-NS_IMPL_ADDREF_INHERITED(HTMLContentElement, Element)
-NS_IMPL_RELEASE_INHERITED(HTMLContentElement, Element)
-
-NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_INHERITED(HTMLContentElement)
-NS_INTERFACE_MAP_END_INHERITING(nsGenericHTMLElement)
-
-NS_IMPL_ELEMENT_CLONE(HTMLContentElement)
-
-JSObject*
-HTMLContentElement::WrapNode(JSContext *aCx, JS::Handle<JSObject*> aGivenProto)
-{
-  return HTMLContentElementBinding::Wrap(aCx, this, aGivenProto);
-}
-
-nsresult
-HTMLContentElement::BindToTree(nsIDocument* aDocument,
-                               nsIContent* aParent,
-                               nsIContent* aBindingParent,
-                               bool aCompileEventHandlers)
-{
-  RefPtr<ShadowRoot> oldContainingShadow = GetContainingShadow();
-
-  nsresult rv = nsGenericHTMLElement::BindToTree(aDocument, aParent,
-                                                 aBindingParent,
-                                                 aCompileEventHandlers);
-  NS_ENSURE_SUCCESS(rv, rv);
-
-  ShadowRoot* containingShadow = GetContainingShadow();
-  if (containingShadow && !oldContainingShadow) {
-    nsINode* parentNode = nsINode::GetParentNode();
-    while (parentNode && parentNode != containingShadow) {
-      if (parentNode->IsHTMLContentElement()) {
-        // Content element in fallback content is not an insertion point.
-        return NS_OK;
-      }
-      parentNode = parentNode->GetParentNode();
-    }
-
-    // If the content element is being inserted into a ShadowRoot,
-    // add this element to the list of insertion points.
-    mIsInsertionPoint = true;
-    containingShadow->AddInsertionPoint(this);
-    containingShadow->SetInsertionPointChanged();
-  }
-
-  return NS_OK;
-}
-
-void
-HTMLContentElement::UnbindFromTree(bool aDeep, bool aNullParent)
-{
-  RefPtr<ShadowRoot> oldContainingShadow = GetContainingShadow();
-
-  nsGenericHTMLElement::UnbindFromTree(aDeep, aNullParent);
-
-  if (oldContainingShadow && !GetContainingShadow() && mIsInsertionPoint) {
-    oldContainingShadow->RemoveInsertionPoint(this);
-
-    // Remove all the matched nodes now that the
-    // insertion point is no longer an insertion point.
-    ClearMatchedNodes();
-    oldContainingShadow->SetInsertionPointChanged();
-
-    mIsInsertionPoint = false;
-  }
-}
-
-void
-HTMLContentElement::AppendMatchedNode(nsIContent* aContent)
-{
-  mMatchedNodes.AppendElement(aContent);
-  nsTArray<nsIContent*>& destInsertionPoint = aContent->DestInsertionPoints();
-  destInsertionPoint.AppendElement(this);
-
-  if (mMatchedNodes.Length() == 1) {
-    // Fallback content gets dropped so we need to updated fallback
-    // content distribution.
-    UpdateFallbackDistribution();
-  }
-}
-
-void
-HTMLContentElement::UpdateFallbackDistribution()
-{
-  for (nsIContent* child = nsINode::GetFirstChild();
-       child;
-       child = child->GetNextSibling()) {
-    nsTArray<nsIContent*>& destInsertionPoint = child->DestInsertionPoints();
-    destInsertionPoint.Clear();
-    if (mMatchedNodes.IsEmpty()) {
-      destInsertionPoint.AppendElement(this);
-    }
-  }
-}
-
-void
-HTMLContentElement::RemoveMatchedNode(nsIContent* aContent)
-{
-  mMatchedNodes.RemoveElement(aContent);
-  ShadowRoot::RemoveDestInsertionPoint(this, aContent->DestInsertionPoints());
-
-  if (mMatchedNodes.IsEmpty()) {
-    // Fallback content is activated so we need to update fallback
-    // content distribution.
-    UpdateFallbackDistribution();
-  }
-}
-
-void
-HTMLContentElement::InsertMatchedNode(uint32_t aIndex, nsIContent* aContent)
-{
-  mMatchedNodes.InsertElementAt(aIndex, aContent);
-  nsTArray<nsIContent*>& destInsertionPoint = aContent->DestInsertionPoints();
-  destInsertionPoint.AppendElement(this);
-
-  if (mMatchedNodes.Length() == 1) {
-    // Fallback content gets dropped so we need to updated fallback
-    // content distribution.
-    UpdateFallbackDistribution();
-  }
-}
-
-void
-HTMLContentElement::ClearMatchedNodes()
-{
-  for (uint32_t i = 0; i < mMatchedNodes.Length(); i++) {
-    ShadowRoot::RemoveDestInsertionPoint(this, mMatchedNodes[i]->DestInsertionPoints());
-  }
-
-  mMatchedNodes.Clear();
-
-  UpdateFallbackDistribution();
-}
-
-static bool
-IsValidContentSelectors(nsCSSSelector* aSelector)
-{
-  nsCSSSelector* currentSelector = aSelector;
-  while (currentSelector) {
-    // Blacklist invalid selector fragments.
-    if (currentSelector->IsPseudoElement() ||
-        currentSelector->mPseudoClassList ||
-        currentSelector->mNegations ||
-        currentSelector->mOperator) {
-      return false;
-    }
-
-    currentSelector = currentSelector->mNext;
-  }
-
-  return true;
-}
-
-nsresult
-HTMLContentElement::AfterSetAttr(int32_t aNamespaceID, nsIAtom* aName,
-                                 const nsAttrValue* aValue,
-                                 const nsAttrValue* aOldValue, bool aNotify)
-{
-  if (aNamespaceID == kNameSpaceID_None && aName == nsGkAtoms::select) {
-    if (aValue) {
-      // Select attribute was updated, the insertion point may match different
-      // elements.
-      nsIDocument* doc = OwnerDoc();
-      nsCSSParser parser(doc->CSSLoader());
-
-      mValidSelector = true;
-      mSelectorList = nullptr;
-
-      nsAutoString valueStr;
-      aValue->ToString(valueStr);
-      nsresult rv = parser.ParseSelectorString(valueStr,
-                                               doc->GetDocumentURI(),
-                                               // Bug 11240
-                                               0, // XXX get the line number!
-                                               getter_Transfers(mSelectorList));
-
-      // We don't want to return an exception if parsing failed because
-      // the spec does not define it as an exception case.
-      if (NS_SUCCEEDED(rv)) {
-        // Ensure that all the selectors are valid
-        nsCSSSelectorList* selectors = mSelectorList;
-        while (selectors) {
-          if (!IsValidContentSelectors(selectors->mSelectors)) {
-            // If we have an invalid selector, we can not match anything.
-            mValidSelector = false;
-            mSelectorList = nullptr;
-            break;
-          }
-          selectors = selectors->mNext;
-        }
-      }
-
-      if (ShadowRoot* containingShadow = GetContainingShadow()) {
-        containingShadow->DistributeAllNodes();
-      }
-    } else {
-      // The select attribute was removed. This insertion point becomes
-      // a universal selector.
-      mValidSelector = true;
-      mSelectorList = nullptr;
-
-      if (ShadowRoot* containingShadow = GetContainingShadow()) {
-        containingShadow->DistributeAllNodes();
-      }
-    }
-  }
-
-  return nsGenericHTMLElement::AfterSetAttr(aNamespaceID, aName, aValue,
-                                            aOldValue, aNotify);
-}
-
-bool
-HTMLContentElement::Match(nsIContent* aContent)
-{
-  if (!mValidSelector) {
-    return false;
-  }
-
-  if (mSelectorList) {
-    nsIDocument* doc = OwnerDoc();
-    ShadowRoot* containingShadow = GetContainingShadow();
-    nsIContent* host = containingShadow->GetHost();
-
-    TreeMatchContext matchingContext(false, nsRuleWalker::eRelevantLinkUnvisited,
-                                     doc, TreeMatchContext::eNeverMatchVisited);
-    doc->FlushPendingLinkUpdates();
-    matchingContext.SetHasSpecifiedScope();
-    matchingContext.AddScopeElement(host->AsElement());
-
-    if (!aContent->IsElement()) {
-      return false;
-    }
-
-    return nsCSSRuleProcessor::SelectorListMatches(aContent->AsElement(),
-                                                   matchingContext,
-                                                   mSelectorList);
-  }
-
-  return true;
-}
-
-already_AddRefed<DistributedContentList>
-HTMLContentElement::GetDistributedNodes()
-{
-  RefPtr<DistributedContentList> list = new DistributedContentList(this);
-  return list.forget();
-}
-
-NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(DistributedContentList, mParent,
-                                      mDistributedNodes)
-
-NS_INTERFACE_TABLE_HEAD(DistributedContentList)
-  NS_WRAPPERCACHE_INTERFACE_TABLE_ENTRY
-  NS_INTERFACE_TABLE(DistributedContentList, nsINodeList, nsIDOMNodeList)
-  NS_INTERFACE_TABLE_TO_MAP_SEGUE_CYCLE_COLLECTION(DistributedContentList)
-NS_INTERFACE_MAP_END
-
-NS_IMPL_CYCLE_COLLECTING_ADDREF(DistributedContentList)
-NS_IMPL_CYCLE_COLLECTING_RELEASE(DistributedContentList)
-
-DistributedContentList::DistributedContentList(HTMLContentElement* aHostElement)
-  : mParent(aHostElement)
-{
-  MOZ_COUNT_CTOR(DistributedContentList);
-
-  if (aHostElement->IsInsertionPoint()) {
-    if (aHostElement->MatchedNodes().IsEmpty()) {
-      // Fallback content.
-      nsINode* contentNode = aHostElement;
-      for (nsIContent* content = contentNode->GetFirstChild();
-           content;
-           content = content->GetNextSibling()) {
-        mDistributedNodes.AppendElement(content);
-      }
-    } else {
-      mDistributedNodes.AppendElements(aHostElement->MatchedNodes());
-    }
-  }
-}
-
-DistributedContentList::~DistributedContentList()
-{
-  MOZ_COUNT_DTOR(DistributedContentList);
-}
-
-nsIContent*
-DistributedContentList::Item(uint32_t aIndex)
-{
-  return mDistributedNodes.SafeElementAt(aIndex);
-}
-
-NS_IMETHODIMP
-DistributedContentList::Item(uint32_t aIndex, nsIDOMNode** aReturn)
-{
-  nsIContent* item = Item(aIndex);
-  if (!item) {
-    return NS_ERROR_FAILURE;
-  }
-
-  return CallQueryInterface(item, aReturn);
-}
-
-NS_IMETHODIMP
-DistributedContentList::GetLength(uint32_t* aLength)
-{
-  *aLength = mDistributedNodes.Length();
-  return NS_OK;
-}
-
-int32_t
-DistributedContentList::IndexOf(nsIContent* aContent)
-{
-  return mDistributedNodes.IndexOf(aContent);
-}
-
-JSObject*
-DistributedContentList::WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto)
-{
-  return NodeListBinding::Wrap(aCx, this, aGivenProto);
-}
-
diff --git a/dom/html/HTMLContentElement.h b/dom/html/HTMLContentElement.h
deleted file mode 100644
index 630e26d17..000000000
--- a/dom/html/HTMLContentElement.h
+++ /dev/null
@@ -1,126 +0,0 @@
-/* -*- 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 mozilla_dom_HTMLContentElement_h__
-#define mozilla_dom_HTMLContentElement_h__
-
-#include "nsAutoPtr.h"
-#include "nsINodeList.h"
-#include "nsGenericHTMLElement.h"
-
-struct nsCSSSelectorList;
-
-namespace mozilla {
-namespace dom {
-
-class DistributedContentList;
-
-class HTMLContentElement final : public nsGenericHTMLElement
-{
-public:
-  explicit HTMLContentElement(already_AddRefed<mozilla::dom::NodeInfo>& aNodeInfo);
-
-  // nsISupports
-  NS_DECL_ISUPPORTS_INHERITED
-
-  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(HTMLContentElement,
-                                           nsGenericHTMLElement)
-
-  NS_IMPL_FROMCONTENT_HELPER(HTMLContentElement, IsHTMLContentElement())
-
-  virtual bool IsHTMLContentElement() const override { return true; }
-
-  virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
-
-  virtual nsIDOMNode* AsDOMNode() override { return this; }
-
-  virtual nsresult BindToTree(nsIDocument* aDocument, nsIContent* aParent,
-                              nsIContent* aBindingParent,
-                              bool aCompileEventHandlers) override;
-
-  virtual void UnbindFromTree(bool aDeep = true,
-                              bool aNullParent = true) override;
-
-  /**
-   * Returns whether if the selector of this insertion point
-   * matches the provided content.
-   */
-  bool Match(nsIContent* aContent);
-  bool IsInsertionPoint() const { return mIsInsertionPoint; }
-  nsCOMArray<nsIContent>& MatchedNodes() { return mMatchedNodes; }
-  void AppendMatchedNode(nsIContent* aContent);
-  void RemoveMatchedNode(nsIContent* aContent);
-  void InsertMatchedNode(uint32_t aIndex, nsIContent* aContent);
-  void ClearMatchedNodes();
-
-  // WebIDL methods.
-  already_AddRefed<DistributedContentList> GetDistributedNodes();
-  void GetSelect(nsAString& aSelect)
-  {
-    Element::GetAttr(kNameSpaceID_None, nsGkAtoms::select, aSelect);
-  }
-  void SetSelect(const nsAString& aSelect)
-  {
-    Element::SetAttr(kNameSpaceID_None, nsGkAtoms::select, aSelect, true);
-  }
-
-protected:
-  virtual ~HTMLContentElement();
-
-  virtual JSObject* WrapNode(JSContext *aCx, JS::Handle<JSObject*> aGivenProto) override;
-
-  /**
-   * Updates the destination insertion points of the fallback
-   * content of this insertion point. If there are nodes matched
-   * to this insertion point, then destination insertion points
-   * of fallback are cleared, otherwise, this insertion point
-   * is a destination insertion point.
-   */
-  void UpdateFallbackDistribution();
-
-  virtual nsresult AfterSetAttr(int32_t aNamespaceID, nsIAtom* aName,
-                                const nsAttrValue* aValue,
-                                const nsAttrValue* aOldValue,
-                                bool aNotify) override;
-
-  /**
-   * An array of nodes from the ShadowRoot host that match the
-   * content insertion selector.
-   */
-  nsCOMArray<nsIContent> mMatchedNodes;
-
-  nsAutoPtr<nsCSSSelectorList> mSelectorList;
-  bool mValidSelector;
-  bool mIsInsertionPoint;
-};
-
-class DistributedContentList : public nsINodeList
-{
-public:
-  explicit DistributedContentList(HTMLContentElement* aHostElement);
-
-  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
-  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(DistributedContentList)
-
-  // nsIDOMNodeList
-  NS_DECL_NSIDOMNODELIST
-
-  // nsINodeList
-  virtual nsIContent* Item(uint32_t aIndex) override;
-  virtual int32_t IndexOf(nsIContent* aContent) override;
-  virtual nsINode* GetParentObject() override { return mParent; }
-  virtual JSObject* WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) override;
-protected:
-  virtual ~DistributedContentList();
-  RefPtr<HTMLContentElement> mParent;
-  nsCOMArray<nsIContent> mDistributedNodes;
-};
-
-} // namespace dom
-} // namespace mozilla
-
-#endif // mozilla_dom_HTMLContentElement_h__
-
diff --git a/dom/html/moz.build b/dom/html/moz.build
index 79554df21..342b027a5 100644
--- a/dom/html/moz.build
+++ b/dom/html/moz.build
@@ -52,7 +52,6 @@ EXPORTS.mozilla.dom += [
     'HTMLBRElement.h',
     'HTMLButtonElement.h',
     'HTMLCanvasElement.h',
-    'HTMLContentElement.h',
     'HTMLDataElement.h',
     'HTMLDataListElement.h',
     'HTMLDetailsElement.h',
@@ -131,7 +130,6 @@ UNIFIED_SOURCES += [
     'HTMLBRElement.cpp',
     'HTMLButtonElement.cpp',
     'HTMLCanvasElement.cpp',
-    'HTMLContentElement.cpp',
     'HTMLDataElement.cpp',
     'HTMLDataListElement.cpp',
     'HTMLDetailsElement.cpp',
diff --git a/dom/tests/mochitest/webcomponents/mochitest.ini b/dom/tests/mochitest/webcomponents/mochitest.ini
index 2cfd747c4..d56196272 100644
--- a/dom/tests/mochitest/webcomponents/mochitest.ini
+++ b/dom/tests/mochitest/webcomponents/mochitest.ini
@@ -25,11 +25,7 @@ skip-if = !debug # TestFunctions only applied in debug builds
 [test_custom_element_define.html]
 [test_custom_element_define_parser.html]
 [test_custom_element_template.html]
-[test_nested_content_element.html]
-[test_dest_insertion_points.html]
-[test_fallback_dest_insertion_points.html]
 [test_detached_style.html]
-[test_dynamic_content_element_matching.html]
 [test_document_adoptnode.html]
 [test_document_importnode.html]
 [test_document_register.html]
diff --git a/dom/tests/mochitest/webcomponents/test_dest_insertion_points.html b/dom/tests/mochitest/webcomponents/test_dest_insertion_points.html
deleted file mode 100644
index 2d4a92ed2..000000000
--- a/dom/tests/mochitest/webcomponents/test_dest_insertion_points.html
+++ /dev/null
@@ -1,73 +0,0 @@
-<!DOCTYPE HTML>
-<html>
-<!--
-https://bugzilla.mozilla.org/show_bug.cgi?id=999999
--->
-<head>
-  <meta charset="utf-8">
-  <title>Test for Bug 999999</title>
-  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
-  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
-</head>
-<body>
-<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=999999">Mozilla Bug 999999</a>
-<p id="display"></p>
-<div id="content">
-<div id="shadowhost">
-</div>
-</div>
-<pre id="test">
-</pre>
-<script type="application/javascript">
-
-/** Test for Bug 999999 **/
-var host = document.getElementById("shadowhost");
-
-// Test destination insertion points of node distributed to content element.
-var shadowRoot = host.createShadowRoot();
-shadowRoot.innerHTML = '<div id="innerhost"><content id="innercontent" select=".red"></content></div>';
-var innerContent = shadowRoot.getElementById("innercontent");
-
-var span = document.createElement("span");
-span.setAttribute("class", "red blue");
-is(host.getDestinationInsertionPoints().length, 0, "Destination insertion points should be empty when not being distributed.");
-
-host.appendChild(span);
-
-is(span.getDestinationInsertionPoints().length, 1, "Destination insertion points should only contain a single content insertion point.");
-is(span.getDestinationInsertionPoints()[0], innerContent, "Content element should contain destination insertion point.");
-
-// Test destination insertion points of redistributed node.
-var innerHost = shadowRoot.getElementById("innerhost");
-var innerShadowRoot = innerHost.createShadowRoot();
-innerShadowRoot.innerHTML = '<content id="innerinnercontent" select=".blue"></content>';
-
-var innerInnerContent = innerShadowRoot.getElementById("innerinnercontent");
-
-is(span.getDestinationInsertionPoints().length, 2, "Redistributed node should have 2 destination insertion points.");
-is(span.getDestinationInsertionPoints()[1], innerInnerContent, "Nested content insertion point should be in list of destination insertion points.");
-
-// Test destination insertion points after removing reprojection onto second content element.
-span.setAttribute("class", "red");
-is(span.getDestinationInsertionPoints().length, 1, "Destination insertion points should only contain 1 insertion point after removing reprojection.");
-is(span.getDestinationInsertionPoints()[0], innerContent, "First content element should be only insertion point after removing reprojection.");
-
-// Test destination insertion points after removing the projected content from the host.
-host.removeChild(span);
-is(span.getDestinationInsertionPoints().length, 0, "Destination insertion points should be empty after being removed from the shadow host.");
-
-// Test destination insertion points of distributed content after removing insertion point.
-var div = document.createElement("div");
-div.setAttribute("class", "red blue");
-host.appendChild(div);
-
-is(div.getDestinationInsertionPoints().length, 2, "Div should be distributed into 2 insertion points.");
-
-innerShadowRoot.removeChild(innerInnerContent);
-
-is(div.getDestinationInsertionPoints().length, 1, "Div should be distributed into insertion point in one ShadowRoot.");
-is(div.getDestinationInsertionPoints()[0], innerContent, "Destination insertion points should only contain content insertion point in first ShadowRoot.");
-
-</script>
-</body>
-</html>
diff --git a/dom/tests/mochitest/webcomponents/test_dynamic_content_element_matching.html b/dom/tests/mochitest/webcomponents/test_dynamic_content_element_matching.html
deleted file mode 100644
index c9af76610..000000000
--- a/dom/tests/mochitest/webcomponents/test_dynamic_content_element_matching.html
+++ /dev/null
@@ -1,50 +0,0 @@
-<!DOCTYPE HTML>
-<html>
-<!--
-https://bugzilla.mozilla.org/show_bug.cgi?id=806506
--->
-<head>
-  <title>Test for dynamic changes to content matching content elements</title>
-  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
-  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
-</head>
-<body>
-<div class="tall" id="bodydiv"></div>
-<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=806506">Bug 806506</a>
-<script>
-// Create ShadowRoot.
-var elem = document.createElement("div");
-var root = elem.createShadowRoot();
-
-var redInsertionPoint = document.createElement("content");
-redInsertionPoint.select = "*[data-color=red]";
-
-var blueInsertionPoint = document.createElement("content");
-blueInsertionPoint.select = "*[data-color=blue]";
-
-root.appendChild(redInsertionPoint);
-root.appendChild(blueInsertionPoint);
-
-is(blueInsertionPoint.getDistributedNodes().length, 0, "Blue insertion point should have no distributed nodes.");
-is(redInsertionPoint.getDistributedNodes().length, 0, "Red insertion point should have no distrubted nodes.");
-
-var matchElement = document.createElement("div");
-matchElement.setAttribute("data-color", "red");
-elem.appendChild(matchElement);
-
-is(blueInsertionPoint.getDistributedNodes().length, 0, "Blue insertion point should have no distributed nodes.");
-is(redInsertionPoint.getDistributedNodes().length, 1, "Red insertion point should match recently inserted div.");
-
-matchElement.setAttribute("data-color", "blue");
-is(blueInsertionPoint.getDistributedNodes().length, 1, "Blue insertion point should match element after changing attribute value.");
-is(redInsertionPoint.getDistributedNodes().length, 0, "Red insertion point should not match element after changing attribute value.");
-
-matchElement.removeAttribute("data-color");
-
-is(blueInsertionPoint.getDistributedNodes().length, 0, "Blue insertion point should have no distributed nodes after removing the matching attribute.");
-is(redInsertionPoint.getDistributedNodes().length, 0, "Red insertion point should have no distrubted nodes after removing the matching attribute.");
-
-</script>
-</body>
-</html>
-
diff --git a/dom/tests/mochitest/webcomponents/test_fallback_dest_insertion_points.html b/dom/tests/mochitest/webcomponents/test_fallback_dest_insertion_points.html
deleted file mode 100644
index 4eefa165f..000000000
--- a/dom/tests/mochitest/webcomponents/test_fallback_dest_insertion_points.html
+++ /dev/null
@@ -1,71 +0,0 @@
-<!DOCTYPE HTML>
-<html>
-<!--
-https://bugzilla.mozilla.org/show_bug.cgi?id=999999
--->
-<head>
-  <meta charset="utf-8">
-  <title>Test for Bug 999999</title>
-  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
-  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
-</head>
-<body>
-<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=999999">Mozilla Bug 999999</a>
-<p id="display"></p>
-<div id="content">
-<div id="shadowhost"></div>
-</div>
-<pre id="test">
-</pre>
-<script type="application/javascript">
-
-/** Test for Bug 999999 **/
-var host = document.getElementById("shadowhost");
-
-// Test destination insertion points of node distributed to content element.
-var shadowRoot = host.createShadowRoot();
-shadowRoot.innerHTML = '<div id="innerhost"><content id="innercontent"></content></div>';
-
-var fallback = document.createElement("span");
-var innerContent = shadowRoot.getElementById("innercontent");
-
-innerContent.appendChild(fallback);
-
-is(fallback.getDestinationInsertionPoints().length, 1, "Active fallback content should be distributed to insertion point.");
-is(fallback.getDestinationInsertionPoints()[0], innerContent, "Insertion point should be in list of destination insertion points.");
-
-// Test destination insertion points of reprojected fallback content.
-var innerHost = shadowRoot.getElementById("innerhost");
-var innerShadowRoot = innerHost.createShadowRoot();
-innerShadowRoot.innerHTML = '<content id="innerinnercontent"></content>';
-
-var innerInnerContent = innerShadowRoot.getElementById("innerinnercontent");
-
-is(fallback.getDestinationInsertionPoints().length, 2, "Fallback content should have been distributed into parent and reprojected into another insertion point.");
-is(fallback.getDestinationInsertionPoints()[1], innerInnerContent, "Destination insertion points should contain content element to which the node was reprojected.");
-
-// Test destination insertion points of fallback content that was dropped due to content element matching a node in the host.
-var span = document.createElement("span");
-host.appendChild(span);
-
-is(fallback.getDestinationInsertionPoints().length, 0, "After dropping insertion points, fallback content should not have any nodes in destination insertion points list.");
-
-// Test destination insertion points of fallback content after reactivating by dropping matched content on host.
-host.removeChild(span);
-is(fallback.getDestinationInsertionPoints().length, 2, "Fallback content should have 2 destination insertion points after being reactivated.");
-is(fallback.getDestinationInsertionPoints()[0], innerContent, "First destination insertion point should be the parent content");
-is(fallback.getDestinationInsertionPoints()[1], innerInnerContent, "Second destination insertion point should be the content to which the node is reprojected.");
-
-// Test destination insertion points of fallback content after removed from the tree.
-innerContent.removeChild(fallback);
-is(fallback.getDestinationInsertionPoints().length, 0, "Fallback content is no longer fallback content, destination insertion points should be empty.");
-
-// Test destination insertion points of child of non-insertion point content element.
-var notInsertionPointContent = document.createElement("content");
-var notFallback = document.createElement("span");
-notInsertionPointContent.appendChild(notFallback);
-is(notFallback.getDestinationInsertionPoints().length, 0, "Child of non-insertion point content should not be distributed to any nodes.");
-
-</script>
-</body>
-</html>
diff --git a/dom/tests/mochitest/webcomponents/test_nested_content_element.html b/dom/tests/mochitest/webcomponents/test_nested_content_element.html
deleted file mode 100644
index 1d98d2996..000000000
--- a/dom/tests/mochitest/webcomponents/test_nested_content_element.html
+++ /dev/null
@@ -1,127 +0,0 @@
-<!DOCTYPE HTML>
-<html>
-<!--
-https://bugzilla.mozilla.org/show_bug.cgi?id=806506
--->
-<head>
-  <title>Test for HTMLContent element</title>
-  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
-  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
-</head>
-<body>
-<div id="grabme"></div>
-<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=806506">Bug 806506</a>
-<script>
-
-/**
- * Constructs a node with a nested ShadowRoot with the following structure:
- * <span> - - - - - - - - - - <ShadowRoot>
- *   <span>                     <span> - - - - - - - - - - <ShadowRoot>
- *    id=one                      id=four                    <span>
- *    data-color=red              data-color=orange            id=eleven
- *   <span>                       <span>                     <content>
- *    id=two                        id=five                    id=twelve
- *    data-color=blue               data-color=purple          select=secondSelect
- *   <span>                       <content>                  <span>
- *    id=three                      id=six                     id=thirteen
- *    data-color=green              select=firstSelect
- *                                  <span>
- *                                    id=seven
- *                                  <content>
- *                                    id=eight
- *                                  <span>
- *                                    id=nine
- *                                <span>
- *                                  id=ten
- *                                  data-color=grey
- */
-function constructTree(firstSelect, secondSelect) {
-  var rootSpan = document.createElement("span");
-  rootSpan.innerHTML = '<span id="one" data-color="red"></span><span id="two" data-color="blue"></span><span id="three" data-color="green"></span>';
-  var firstShadow = rootSpan.createShadowRoot();
-  firstShadow.innerHTML = '<span id="four" data-color="orange"><span id="five" data-color="purple"></span><content id="six" select="' + firstSelect + '"><span id="seven"></span><content id="eight"></content><span id="nine"></span></content><span id="ten"></span></span>';
-  var secondShadow = firstShadow.firstChild.createShadowRoot();
-  secondShadow.innerHTML = '<span id="eleven"></span><content id="twelve" select="' + secondSelect + '"></content><span id="thirteen"></span>';
-  return rootSpan;
-}
-
-// Create a tree with content that matches on everything and check node distribution.
-var allSpan = constructTree("*", "*");
-var firstContent = allSpan.shadowRoot.getElementById("six");
-var firstDistNodes = firstContent.getDistributedNodes();
-is(firstDistNodes.length, 3, "Universal selector should match all nodes.");
-// Check the order of the distributed nodes.
-is(firstDistNodes.item(0).id, "one", "First distributed node should have id of 'one'");
-is(firstDistNodes.item(1).id, "two", "Second distributed node should have id of 'two'");
-is(firstDistNodes.item(2).id, "three", "Third distributed node should have id of 'three'");
-var secondContent = allSpan.shadowRoot.firstChild.shadowRoot.getElementById("twelve");
-var secondDistNodes = secondContent.getDistributedNodes();
-is(secondDistNodes.length, 5, "Universial selector should match all nodes including those distributed into content.");
-// Check the order of the distribute nodes.
-is(secondDistNodes.item(0).id, "five", "First distributed node should have id of 'five'");
-is(secondDistNodes.item(1).id, "one", "Second distributed (reprojected) node should have id of 'one'");
-is(secondDistNodes.item(2).id, "two", "Third distributed (reprojected) node should have id of 'two'");
-is(secondDistNodes.item(3).id, "three", "Fourth distributed (reprojected) node should have id of 'three'");
-is(secondDistNodes.item(4).id, "ten", "Fifth distributed node should have id of 'ten'");
-
-// Append an element after id=two and make sure that it is inserted into the corrent
-// position in the insertion points.
-var additionalSpan = document.createElement("span");
-additionalSpan.id = "additional";
-
-// Insert the additional span in the third position, before the span with id=three.
-allSpan.insertBefore(additionalSpan, allSpan.childNodes.item(2));
-firstDistNodes = firstContent.getDistributedNodes();
-secondDistNodes = secondContent.getDistributedNodes();
-is(firstDistNodes.length, 4, "First insertion point should match one more node.");
-is(firstDistNodes.item(2).id, "additional", "Additional span should have been inserted into the third position of the first insertion point.");
-
-is(secondDistNodes.length, 6, "Second insertion point should match one more node.");
-is(secondDistNodes.item(3).id, "additional", "Additional span should have been inserted into the fourth position of the second insertion point.");
-
-function nodeListDoesNotContain(nodeList, element) {
-  for (var i = 0; i < nodeList.length; i++) {
-    if (nodeList[i] == element) {
-      return false;
-    }
-  }
-  return true;
-}
-
-// Remove the span with id=one and check that it is removed from all insertion points.
-allSpan = constructTree("*", "*");
-var spanOne = allSpan.firstChild;
-allSpan.removeChild(spanOne);
-firstContent = allSpan.shadowRoot.getElementById("six");
-ok(nodeListDoesNotContain(firstContent.getDistributedNodes(), spanOne), "Child removed from host should not appear in insertion point node list.");
-secondContent = allSpan.shadowRoot.firstChild.shadowRoot.getElementById("twelve");
-ok(nodeListDoesNotContain(secondContent.getDistributedNodes(), spanOne), "Child removed from host should not appear in nested insertion point node list.");
-
-// Make sure <content> in fallback content is inactive.
-// First insertion point will not match anything and will use fallback content.
-allSpan = constructTree("#nomatch", "*");
-var fallbackInsertionPoint = allSpan.shadowRoot.getElementById("eight");
-is(fallbackInsertionPoint.getDistributedNodes().length, 0, "Insertion points in default content should be inactive.");
-
-// Insertion points with non-universal selectors.
-allSpan = constructTree("span[data-color=blue]", "*");
-firstContent = allSpan.shadowRoot.getElementById("six");
-is(firstContent.getDistributedNodes().length, 1, "Insertion point selector should only match one node.");
-is(firstContent.getDistributedNodes()[0].dataset.color, "blue", "Projected node should match selector.");
-secondContent = allSpan.shadowRoot.firstChild.shadowRoot.getElementById("twelve");
-is(secondContent.getDistributedNodes().length, 3, "Second insertion point should match two children and one reprojected node.");
-is(secondContent.getDistributedNodes()[1].dataset.color, "blue", "Projected node should match selector.");
-
-allSpan = constructTree("span[data-color=blue]", "span[data-color=blue]");
-firstContent = allSpan.shadowRoot.getElementById("six");
-is(firstContent.getDistributedNodes().length, 1, "Insertion point selector should only match one node.");
-is(firstContent.getDistributedNodes()[0].dataset.color, "blue", "Projected node should match selector.");
-secondContent = allSpan.shadowRoot.firstChild.shadowRoot.getElementById("twelve");
-is(secondContent.getDistributedNodes().length, 1, "Insertion point should only match reprojected node.");
-is(secondContent.getDistributedNodes()[0].dataset.color, "blue", "Projected node should match selector.");
-
-// Make sure that dynamically appended default content will get distributed.
-</script>
-</body>
-</html>
-
diff --git a/dom/webidl/HTMLContentElement.webidl b/dom/webidl/HTMLContentElement.webidl
deleted file mode 100644
index ea809f120..000000000
--- a/dom/webidl/HTMLContentElement.webidl
+++ /dev/null
@@ -1,20 +0,0 @@
-/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* 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/.
- *
- * The origin of this IDL file is
- * https://dvcs.w3.org/hg/webcomponents/raw-file/tip/spec/shadow/index.html
- *
- * © Copyright 2004-2011 Apple Computer, Inc., Mozilla Foundation, and
- * Opera Software ASA. You are granted a license to use, reproduce
- * and create derivative works of this document.
- */
-
-[Func="nsDocument::IsWebComponentsEnabled"]
-interface HTMLContentElement : HTMLElement
-{
-  attribute DOMString select;
-  NodeList getDistributedNodes();
-};
-
diff --git a/dom/webidl/moz.build b/dom/webidl/moz.build
index ae97bbb30..d76a58e1f 100644
--- a/dom/webidl/moz.build
+++ b/dom/webidl/moz.build
@@ -177,7 +177,6 @@ WEBIDL_FILES = [
     'HTMLButtonElement.webidl',
     'HTMLCanvasElement.webidl',
     'HTMLCollection.webidl',
-    'HTMLContentElement.webidl',
     'HTMLDataElement.webidl',
     'HTMLDataListElement.webidl',
     'HTMLDetailsElement.webidl',
-- 
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