Fix clippingContainer for fixed position elements

Source/core/rendering/RenderObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 797 matching lines @@
         while (o && ((o->isInline() && !o->isReplaced()) || !o->isRenderBlock()))
             o = o->parent();
     }
 
     if (!o || !o->isRenderBlock())
         return 0; // This can still happen in case of an orphaned tree
 
     return toRenderBlock(o);
 }
 
-RenderObject* RenderObject::clippingContainer() const
+RenderObject* RenderObject::clippingContainer()
 {
-    for (RenderObject* container = containingBlock(); container; container = container->containingBlock()) {
+    RenderObject* container = this;

[ojan, 2014/02/26 20:55:27]

Had to remove the const for this line. I think I could do some shenanigans with
having a const renderer local variable and a non-const container local variable
to keep the const, but that seemed not worth it.

+    while (container) {
+        if (container->style()->position() == FixedPosition) {
+            for (container = container->parent(); container && !container->canContainFixedPositionObjects(); container = container->parent()) {

[esprehn, 2014/02/26 21:26:02]

Is this right? Now if you run into something that claims it can contain fixed
position objects we'll use the hasClipOrOverflowClip() check below.

If I do <div style="overflow: hidden; transform: translateZ(0)">
  <div style="position: fixed;"></div>
</div>

will the fixed thing really be clipped by the transformed overflow thing?

+                // CSS clip applies to fixed position elements even for ancestors that are not what the
+                // fixed element is positioned with respect to.
+                if (container->hasClip())
+                    return container;
+            }
+        } else {
+            container = container->containingBlock();
+        }
+
+        if (!container)
+            return 0;
         if (container->hasClipOrOverflowClip())
             return container;
     }
     return 0;
 }
 
 static bool mustRepaintFillLayers(const RenderObject* renderer, const FillLayer* layer)
 {
     // Nobody will use multiple layers without wanting fancy positioning.
     if (layer->next())
@@ skipping 2508 matching lines @@
 {
     if (object1) {
         const WebCore::RenderObject* root = object1;
         while (root->parent())
             root = root->parent();
         root->showRenderTreeAndMark(object1, "*", object2, "-", 0);
     }
 }
 
 #endif