Use float for scroll offset.

third_party/WebKit/Source/platform/graphics/GraphicsLayer.cpp

 /*
  * Copyright (C) 2009 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 1160 matching lines @@
   // WebViewImpl explicitly rather than via GraphicsLayer::didScroll since it
   // needs to be set in tandem with the page scale delta.
   if (isVisualViewport)
     m_layer->layer()->setScrollClient(0);
   else
     m_layer->layer()->setScrollClient(this);
 }
 
 void GraphicsLayer::didScroll() {
   if (m_scrollableArea) {
-    DoublePoint newPosition =
-        -m_scrollableArea->scrollOrigin() +
-        toDoubleSize(m_layer->layer()->scrollPositionDouble());
+    ScrollOffset newOffset = toScrollOffset(-m_scrollableArea->scrollOrigin()) +
+                             m_layer->layer()->scrollOffset();
 
     // FrameView::setScrollPosition doesn't work for compositor commits (interacts poorly with programmatic scroll animations)
     // so we need to use the ScrollableArea version. The FrameView method should go away soon anyway.

[bokan, 2016/10/02 19:47:51]

Remove comment

[szager1, 2016/10/05 07:43:36]

Done.

-    m_scrollableArea->ScrollableArea::setScrollPosition(newPosition,
-                                                        CompositorScroll);
+    m_scrollableArea->setScrollOffset(newOffset, CompositorScroll);
   }
 }
 
 std::unique_ptr<base::trace_event::ConvertableToTraceFormat>
 GraphicsLayer::TakeDebugInfo(cc::Layer* layer) {
   std::unique_ptr<base::trace_event::TracedValue> tracedValue(
       m_debugInfo.asTracedValue());
   tracedValue->SetString(
       "layer_name", WTF::StringUTF8Adaptor(debugName(layer)).asStringPiece());
   return std::move(tracedValue);
@@ skipping 133 matching lines @@
 void showGraphicsLayerTree(const blink::GraphicsLayer* layer) {
   if (!layer) {
     fprintf(stderr, "Cannot showGraphicsLayerTree for (nil).\n");
     return;
   }
 
   String output = layer->layerTreeAsText(blink::LayerTreeIncludesDebugInfo);
   fprintf(stderr, "%s\n", output.utf8().data());
 }
 #endif