Make compositor and blink talk in fractional scroll offset

Source/platform/graphics/GraphicsLayerTest.cpp

 /*
  * Copyright (C) 2012 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
  *     notice, this list of conditions and the following disclaimer in the
@@ skipping 139 matching lines @@
 
 private:
     IntPoint m_scrollPosition;
 };
 
 TEST_F(GraphicsLayerTest, applyScrollToScrollableArea)
 {
     FakeScrollableArea scrollableArea;
     m_graphicsLayer->setScrollableArea(&scrollableArea, false);
 
-    WebPoint scrollPosition(7, 9);
-    m_platformLayer->setScrollPosition(scrollPosition);
+    WebDoublePoint scrollPosition(7, 9);

[Rick Byers, 2014/10/04 00:04:24]

Can you change these to be fractional, just to verify there isn't truncation
happening somewhere here?

[Yufeng Shen (Slow to review), 2014/10/06 17:54:58]

Done.

+    m_platformLayer->setScrollPositionDouble(scrollPosition);
     m_graphicsLayer->didScroll();
 
-    EXPECT_EQ(scrollPosition, WebPoint(scrollableArea.scrollPosition()));
+    EXPECT_EQ(scrollPosition.x, scrollableArea.scrollPositionDouble().x());
+    EXPECT_EQ(scrollPosition.y, scrollableArea.scrollPositionDouble().y());
 }
 
 } // namespace