Preserve fractional scroll offset for JS scrolling API

Source/core/html/ImageDocument.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2010 Apple 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 246 matching lines @@
 
     m_shouldShrinkImage = !m_shouldShrinkImage;
 
     if (m_shouldShrinkImage)
         windowSizeChanged(ScaleZoomedDocument);
     else {
         restoreImageSize(ScaleZoomedDocument);
 
         updateLayout();
 
-        float scale = this->scale();
+        double scale = this->scale();
 
-        int scrollX = static_cast<int>(x / scale - (float)frame()->view()->width() / 2);
-        int scrollY = static_cast<int>(y / scale - (float)frame()->view()->height() / 2);
+        double scrollX = x / scale - static_cast<double>(frame()->view()->width()) / 2;
+        double scrollY = y / scale - static_cast<double>(frame()->view()->height()) / 2;
 
-        frame()->view()->setScrollPosition(IntPoint(scrollX, scrollY));
+        frame()->view()->setScrollPosition(DoublePoint(scrollX, scrollY));
     }
 }
 
 void ImageDocument::imageUpdated()
 {
     ASSERT(m_imageElement);
 
     if (m_imageSizeIsKnown)
         return;
 
@@ skipping 113 matching lines @@
 }
 
 bool ImageEventListener::operator==(const EventListener& listener)
 {
     if (const ImageEventListener* imageEventListener = ImageEventListener::cast(&listener))
         return m_doc == imageEventListener->m_doc;
     return false;
 }
 
 }