Bug 1321284 - Part 1: Make StyleChildrenIterator skip NAC generated by root element primary frame ancestors. r=bholley

MozReview-Commit-ID: HICYWQgkE77

--HG--
extra : rebase_source : 7c5a533ada4eaa9839ca0497426f2c9c2a2d6c0b

dom/base/ChildIterator.cpp

@@ -383,7 +383,10 @@ AllChildrenIterator::AppendNativeAnonymousChildren()
 
   // The root scroll frame is not the primary frame of the root element.
   // Detect and handle this case.
-  if (mOriginalContent == mOriginalContent->OwnerDoc()->GetRootElement()) {
+  //
+  // XXXheycam This probably needs to find the nsCanvasFrame's NAC too.
+  if (!(mFlags & nsIContent::eSkipDocumentLevelNativeAnonymousContent) &&
+      mOriginalContent == mOriginalContent->OwnerDoc()->GetRootElement()) {
     nsIPresShell* presShell = mOriginalContent->OwnerDoc()->GetShell();
     nsIFrame* scrollFrame = presShell ? presShell->GetRootScrollFrame() : nullptr;
     if (scrollFrame) {
@@ -585,12 +588,6 @@ StyleChildrenIterator::IsNeeded(const Element* aElement)
     return true;
   }
 
-  // The root element has a scroll frame that is not the primary frame, so we
-  // need to do special checking for that case.
-  if (aElement == aElement->OwnerDoc()->GetRootElement()) {
-    return true;
-  }
-
   return false;
 }
 

dom/base/ChildIterator.h

@@ -256,18 +256,22 @@ private:
 /**
  * StyleChildrenIterator traverses the children of the element from the
  * perspective of the style system, particularly the children we need to traverse
- * during restyle. This is identical to AllChildrenIterator with eAllChildren,
- * _except_ that we detect and skip any native anonymous children that are used
- * to implement pseudo-elements (since the style system needs to cascade those
- * using different algorithms).
+ * during restyle. This is identical to AllChildrenIterator with
+ * (eAllChildren | eSkipDocumentLevelNativeAnonymousContent), _except_ that we
+ * detect and skip any native anonymous children that are used to implement
+ * pseudo-elements (since the style system needs to cascade those using
+ * different algorithms).
  *
  * Note: it assumes that no mutation of the DOM or frame tree takes place during
  * iteration, and will break horribly if that is not true.
  */
-class StyleChildrenIterator : private AllChildrenIterator {
+class StyleChildrenIterator : private AllChildrenIterator
+{
 public:
   explicit StyleChildrenIterator(const nsIContent* aContent)
-    : AllChildrenIterator(aContent, nsIContent::eAllChildren)
+    : AllChildrenIterator(aContent,
+                          nsIContent::eAllChildren |
+                          nsIContent::eSkipDocumentLevelNativeAnonymousContent)
   {
     MOZ_COUNT_CTOR(StyleChildrenIterator);
   }

dom/base/nsIContent.h

@@ -145,7 +145,14 @@ public:
      * Skip native anonymous content created for placeholder of HTML input,
      * used in conjunction with eAllChildren or eAllButXBL.
      */
-    eSkipPlaceholderContent = 2
+    eSkipPlaceholderContent = 2,
+
+    /**
+     * Skip native anonymous content created by ancestor frames of the root
+     * element's primary frame, such as scrollbar elements created by the root
+     * scroll frame.
+     */
+    eSkipDocumentLevelNativeAnonymousContent = 4,
   };
 
   /**

layout/generic/nsIAnonymousContentCreator.h

@@ -66,7 +66,9 @@ public:
    * Appends "native" anonymous children created by CreateAnonymousContent()
    * to the given content list depending on the filter.
    *
-   * @see nsIContent::GetChildren for set of values used for filter.
+   * @see nsIContent::GetChildren for set of values used for filter.  Currently,
+   *   eSkipPlaceholderContent is the only flag that any implementation of
+   *   this method heeds.
    */
   virtual void AppendAnonymousContentTo(nsTArray<nsIContent*>& aElements,
                                         uint32_t aFilter) = 0;