Preserve fractional scroll offset for JS scrolling API

Source/core/frame/PinchViewport.cpp

 /*
  * Copyright (C) 2013 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 118 matching lines @@
 void PinchViewport::scrollIntoView(const FloatRect& rect)
 {
     if (!mainFrame() || !mainFrame()->view())
         return;
 
     FrameView* view = mainFrame()->view();
 
     float centeringOffsetX = (visibleRect().width() - rect.width()) / 2;
     float centeringOffsetY = (visibleRect().height() - rect.height()) / 2;
 
-    FloatPoint targetOffset(
+    DoublePoint targetOffset(
         rect.x() - centeringOffsetX - visibleRect().x(),
         rect.y() - centeringOffsetY - visibleRect().y());
 
-    view->setScrollPosition(flooredIntPoint(targetOffset));
+    view->setScrollPosition(targetOffset);
 
-    FloatPoint remainder = FloatPoint(targetOffset - view->scrollPosition());
-    move(remainder);
+    DoublePoint remainder = DoublePoint(targetOffset - view->scrollPositionDouble());
+    move(toFloatPoint(remainder));
 }
 
 void PinchViewport::setLocation(const FloatPoint& newLocation)
 {
     setScaleAndLocation(m_scale, newLocation);
 }
 
 void PinchViewport::move(const FloatPoint& delta)
 {
     setLocation(m_offset + delta);
@@ skipping 318 matching lines @@
     } else if (graphicsLayer == m_overlayScrollbarVertical.get()) {
         name =  "Overlay Scrollbar Vertical Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink