Implement <video controls> dodging for text track layout

Source/core/layout/LayoutMedia.cpp

 /*
  * Copyright (C) 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 39 matching lines @@
 void LayoutMedia::layout()
 {
     LayoutSize oldSize = contentBoxRect().size();
 
     LayoutImage::layout();
 
     LayoutSize newSize = contentBoxRect().size();
 
     LayoutState state(*this, locationOffset());
 
-    for (LayoutObject* child = m_children.firstChild(); child; child = child->nextSibling()) {
-        ASSERT(child->node()->isMediaControls() || child->node()->isTextTrackContainer());
+    // Iterate the children in reverse order so that the media controls are laid
+    // out before the text track container. This is to ensure that the text
+    // track rendering has an up-to-date position of the media controls for
+    // overlap checking, see LayoutVTTCue.
+#if ENABLE(ASSERT)
+    bool seenTextTrackContainer = false;
+#endif
+    for (LayoutObject* child = m_children.lastChild(); child; child = child->previousSibling()) {
+#if ENABLE(ASSERT)
+        if (child->node()->isMediaControls())
+            ASSERT(!seenTextTrackContainer);
+        else if (child->node()->isTextTrackContainer())
+            seenTextTrackContainer = true;
+        else
+            ASSERT_NOT_REACHED();
+#endif
 
         if (newSize == oldSize && !child->needsLayout())
             continue;
 
         LayoutBox* layoutBox = toLayoutBox(child);
         layoutBox->setLocation(LayoutPoint(borderLeft(), borderTop()) + LayoutSize(paddingLeft(), paddingTop()));
         // TODO(philipj): Remove the mutableStyleRef() and depend on CSS
         // width/height: inherit to match the media element size.
         layoutBox->mutableStyleRef().setHeight(Length(newSize.height(), Fixed));
         layoutBox->mutableStyleRef().setWidth(Length(newSize.width(), Fixed));
@@ skipping 22 matching lines @@
         return true;
 
     return false;
 }
 
 void LayoutMedia::paintReplaced(const PaintInfo&, const LayoutPoint&)
 {
 }
 
 } // namespace blink