Bug 1505887 - Fix FindChromeAccessOnlySubtreeOwner so that we handle UA widget being ChromeOnlyAccess root. r=smaug

A single video controls test crashed without this, while dereferencing
a null anonOwnerRelated in:

  https://searchfox.org/mozilla-central/rev/c0b26c40769a1e5607a1ae8be37fe64df64fc55e/dom/base/FragmentOrElement.cpp#964

I think this is the right fix for it, but the code that uses this is kind of
complex, so worth double-checking... :)

dom/base/FragmentOrElement.cpp

@@ -883,17 +883,18 @@ FragmentOrElement::GetChildren(uint32_t aFilter)
   return list.forget();
 }
 
-static nsIContent*
-FindChromeAccessOnlySubtreeOwner(nsIContent* aContent)
+static nsINode*
+FindChromeAccessOnlySubtreeOwner(nsINode* aNode)
 {
-  if (aContent->ChromeOnlyAccess()) {
-    bool chromeAccessOnly = false;
-    while (aContent && !chromeAccessOnly) {
-      chromeAccessOnly = aContent->IsRootOfChromeAccessOnlySubtree();
-      aContent = aContent->GetParent();
-    }
+  if (!aNode->ChromeOnlyAccess()) {
+    return aNode;
   }
-  return aContent;
+
+  while (aNode && !aNode->IsRootOfChromeAccessOnlySubtree()) {
+    aNode = aNode->GetParentNode();
+  }
+
+  return aNode ? aNode->GetParentOrHostNode() : nullptr;
 }
 
 already_AddRefed<nsINode>
@@ -904,11 +905,7 @@ FindChromeAccessOnlySubtreeOwner(EventTarget* aTarget)
     return node.forget();
   }
 
-  if (!node->IsContent()) {
-    return nullptr;
-  }
-
-  node = FindChromeAccessOnlySubtreeOwner(node->AsContent());
+  node = FindChromeAccessOnlySubtreeOwner(node);
   return node.forget();
 }
 
@@ -951,9 +948,9 @@ nsIContent::GetEventTargetParent(EventChainPreVisitor& aVisitor)
           (aVisitor.mEvent->mOriginalTarget == this &&
            (aVisitor.mRelatedTargetIsInAnon =
             relatedTarget->ChromeOnlyAccess()))) {
-        nsIContent* anonOwner = FindChromeAccessOnlySubtreeOwner(this);
+        nsINode* anonOwner = FindChromeAccessOnlySubtreeOwner(this);
         if (anonOwner) {
-          nsIContent* anonOwnerRelated =
+          nsINode* anonOwnerRelated =
             FindChromeAccessOnlySubtreeOwner(relatedTarget);
           if (anonOwnerRelated) {
             // Note, anonOwnerRelated may still be inside some other

dom/base/nsIContent.h

@@ -178,26 +178,6 @@ public:
    */
   virtual already_AddRefed<nsINodeList> GetChildren(uint32_t aFilter) = 0;
 
-  /**
-   * Get whether this content is C++-generated anonymous content
-   * @see nsIAnonymousContentCreator
-   * @return whether this content is anonymous
-   */
-  bool IsRootOfNativeAnonymousSubtree() const
-  {
-    NS_ASSERTION(!HasFlag(NODE_IS_NATIVE_ANONYMOUS_ROOT) ||
-                 (HasFlag(NODE_IS_ANONYMOUS_ROOT) &&
-                  HasFlag(NODE_IS_IN_NATIVE_ANONYMOUS_SUBTREE)),
-                 "Some flags seem to be missing!");
-    return HasFlag(NODE_IS_NATIVE_ANONYMOUS_ROOT);
-  }
-
-  bool IsRootOfChromeAccessOnlySubtree() const
-  {
-    return HasFlag(NODE_IS_NATIVE_ANONYMOUS_ROOT |
-                   NODE_IS_ROOT_OF_CHROME_ONLY_ACCESS);
-  }
-
   /**
    * Makes this content anonymous
    * @see nsIAnonymousContentCreator

dom/base/nsINode.h

@@ -1232,6 +1232,26 @@ public:
     return HasFlag(NODE_IS_IN_SHADOW_TREE);
   }
 
+  /**
+   * Get whether this node is C++-generated anonymous content
+   * @see nsIAnonymousContentCreator
+   * @return whether this content is anonymous
+   */
+  bool IsRootOfNativeAnonymousSubtree() const
+  {
+    NS_ASSERTION(!HasFlag(NODE_IS_NATIVE_ANONYMOUS_ROOT) ||
+                 (HasFlag(NODE_IS_ANONYMOUS_ROOT) &&
+                  HasFlag(NODE_IS_IN_NATIVE_ANONYMOUS_SUBTREE)),
+                 "Some flags seem to be missing!");
+    return HasFlag(NODE_IS_NATIVE_ANONYMOUS_ROOT);
+  }
+
+  bool IsRootOfChromeAccessOnlySubtree() const
+  {
+    return HasFlag(NODE_IS_NATIVE_ANONYMOUS_ROOT |
+                   NODE_IS_ROOT_OF_CHROME_ONLY_ACCESS);
+  }
+
   /**
    * Returns true if |this| node is the common ancestor of the start/end
    * nodes of a Range in a Selection or a descendant of such a common ancestor.