Set up clip and scroll parents on the blink side.

public/platform/WebLayer.h

Index: public/platform/WebLayer.h
diff --git a/public/platform/WebLayer.h b/public/platform/WebLayer.h
index 8c6a92d9e7919c3f99cdfbc127b74ca4e8b202d9..294f66acc8afba4318504d15b82781f41ef585df 100644
--- a/public/platform/WebLayer.h
+++ b/public/platform/WebLayer.h
@@ -167,6 +167,16 @@ public:
     // 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
+    // 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*) { }
+
     // Transfers all animations running on the current layer.
     virtual void transferAnimationsTo(WebLayer*) { }