Preserve fractional scroll offset for JS scrolling API

Source/core/frame/LocalDOMWindow.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  *
  * 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 1342 matching lines @@
 {
     if (!isCurrentlyDisplayedInFrame())
         return;
 
     document()->updateLayoutIgnorePendingStylesheets();
 
     FrameView* view = m_frame->view();
     if (!view)
         return;
 
-    IntSize scaledOffset(static_cast<int>(x * m_frame->pageZoomFactor()), static_cast<int>(y * m_frame->pageZoomFactor()));
+    DoubleSize scaledOffset(x * m_frame->pageZoomFactor(), y * m_frame->pageZoomFactor());
     view->scrollBy(scaledOffset, scrollBehavior);
 }
 
 void LocalDOMWindow::scrollBy(double x, double y, const ScrollOptions& scrollOptions, ExceptionState &exceptionState) const
 {
     ScrollBehavior scrollBehavior = ScrollBehaviorAuto;
     if (!scrollBehaviorFromScrollOptions(scrollOptions, scrollBehavior, exceptionState))
         return;
     scrollBy(x, y, scrollBehavior);
 }
 
 void LocalDOMWindow::scrollTo(double x, double y, ScrollBehavior scrollBehavior) const
 {
     if (!isCurrentlyDisplayedInFrame())
         return;
 
     document()->updateLayoutIgnorePendingStylesheets();
 
     RefPtr<FrameView> view = m_frame->view();
     if (!view)
         return;
 
-    IntPoint layoutPos(static_cast<int>(x * m_frame->pageZoomFactor()), static_cast<int>(y * m_frame->pageZoomFactor()));
+    DoublePoint layoutPos(x * m_frame->pageZoomFactor(), y * m_frame->pageZoomFactor());
     view->setScrollPosition(layoutPos, scrollBehavior);
 }
 
 void LocalDOMWindow::scrollTo(double x, double y, const ScrollOptions& scrollOptions, ExceptionState& exceptionState) const
 {
     ScrollBehavior scrollBehavior = ScrollBehaviorAuto;
     if (!scrollBehaviorFromScrollOptions(scrollOptions, scrollBehavior, exceptionState))
         return;
     scrollTo(x, y, scrollBehavior);
 }
@@ skipping 502 matching lines @@
     FrameDestructionObserver::trace(visitor);
 }
 
 v8::Handle<v8::Object> LocalDOMWindow::wrap(v8::Handle<v8::Object> creationContext, v8::Isolate* isolate)
 {
     ASSERT_NOT_REACHED(); // LocalDOMWindow has [Custom=ToV8].
     return v8::Handle<v8::Object>();
 }
 
 } // namespace blink