Use float for scroll offset.

third_party/WebKit/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 140 matching lines @@
   // delta and offset even though it will not be a descendant of the scroll
   // in the layer hierarchy.
   virtual void setScrollParent(WebLayer*) = 0;
 
   // 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*) = 0;
 
   // Scrolling
-  virtual void setScrollPositionDouble(WebDoublePoint) = 0;
-  virtual WebDoublePoint scrollPositionDouble() const = 0;
+  virtual void setScrollOffset(WebFloatSize) = 0;
+  virtual WebFloatSize scrollOffset() const = 0;
 
   // To set a WebLayer as scrollable we must specify the corresponding clip layer.
   virtual void setScrollClipLayer(WebLayer*) = 0;
   virtual bool scrollable() const = 0;
   virtual void setUserScrollable(bool horizontal, bool vertical) = 0;
   virtual bool userScrollableHorizontal() const = 0;
   virtual bool userScrollableVertical() const = 0;
 
   // Indicates that this layer will always scroll on the main thread for the provided reason.
   virtual void addMainThreadScrollingReasons(uint32_t) = 0;
@@ skipping 41 matching lines @@
 
   virtual void setCompositorMutableProperties(uint32_t) = 0;
   virtual uint32_t compositorMutableProperties() const = 0;
 
   virtual void setHasWillChangeTransformHint(bool) = 0;
 };
 
 }  // namespace blink
 
 #endif  // WebLayer_h