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;

[philipj_slow, 2015/03/20 05:58:19]

What do you think, way overkill? If you prefer I could take your advice and
first find the children, then layout them in the wanted order. It'd probably
still be a for-loop though, when I tried just peeking at first firstChild and
lastChild it wasn't really make it clearer.

[fs, 2015/03/20 09:58:54]

I don't mind that much, but it does give the impression of being more generic
than it actually is. All the ifdeffing is kind of ugly though...

[philipj_slow, 2015/03/20 16:46:33]

Yeah, it's ugly alright. I've tinkered a bit on a follow-up and will send that
out, but leave it like this in this CL.

+#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()));
         layoutBox->style()->setHeight(Length(newSize.height(), Fixed));
         layoutBox->style()->setWidth(Length(newSize.width(), Fixed));
         layoutBox->forceLayout();
     }
@@ skipping 20 matching lines @@
         return true;
 
     return false;
 }
 
 void LayoutMedia::paintReplaced(const PaintInfo&, const LayoutPoint&)
 {
 }
 
 } // namespace blink