Set up clip and scroll parents on the blink side.

public/platform/WebLayer.h

 /*
  * Copyright (C) 2011 Google 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
@@ skipping 144 matching lines @@
     virtual void pauseAnimation(int animationId, double timeOffset) = 0;
 
     // The following functions suspend and resume all animations. The given time
     // is assumed to use the same time base as monotonicallyIncreasingTime().
     virtual void suspendAnimations(double monotonicTime) = 0;
     virtual void resumeAnimations(double monotonicTime) = 0;
 
     // Returns true if this layer has any active animations - useful for tests.
     virtual bool hasActiveAnimation() = 0;
 
+    // If a scroll parent is set, this layer will inherit its parent's scroll
+    // delta and offset even though it will not be a descendant of the scroll

[enne (OOO), 2013/08/22 20:54:30]

"its parent's" => "its scroll parent's"?
"of the scroll" => "of the scroll parent"?
"will not" => "may not"?

Doesn't it just inherit the scroll parent's scroll delta and assumes that its
position already includes its scroll parent's offset?

+    // in the layer hierarchy.
+    virtual void setScrollParent(WebLayer*) { }
+
+    // A layer will not respect any clips established by layers between it and
+    // its nearest clipping ancestor. Note, the clip parent must be an ancestor.
+    // This is not a requirement of the scroll parent.
+    virtual void setClipParent(WebLayer*) { }
+
     // Scrolling
     virtual void setScrollPosition(WebPoint) = 0;
     virtual WebPoint scrollPosition() const = 0;
 
     virtual void setMaxScrollPosition(WebSize) = 0;
     virtual WebSize maxScrollPosition() const = 0;
 
     virtual void setScrollable(bool) = 0;
     virtual bool scrollable() const = 0;
 
@@ skipping 30 matching lines @@
 
     // True if the layer is not part of a tree attached to a WebLayerTreeView.
     virtual bool isOrphan() const = 0;
 
     virtual void setWebLayerClient(WebLayerClient*) = 0;
 };
 
 } // namespace WebKit
 
 #endif // WebLayer_h