Fix smooth scroll jump when switching scroll handling between MT and CC

third_party/WebKit/Source/web/PageOverlay.cpp

 /*
  * Copyright (C) 2011 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.
  *
@@ skipping 67 matching lines @@
         return;
 
     if (!m_layer) {
         m_layer = GraphicsLayer::create(m_viewImpl->graphicsLayerFactory(), this);
         m_layer->setDrawsContent(true);
 
         if (WebDevToolsAgentImpl* devTools = m_viewImpl->mainFrameDevToolsAgentImpl())
             devTools->willAddPageOverlay(m_layer.get());
 
         // This is required for contents of overlay to stay in sync with the page while scrolling.
-        WebLayer* platformLayer = m_layer->platformLayer();
-        platformLayer->addMainThreadScrollingReasons(MainThreadScrollingReason::kPageOverlay);
+        m_layer->setMainThreadScrollingReasons(MainThreadScrollingReason::kPageOverlay);
         page->frameHost().visualViewport().containerLayer()->addChild(m_layer.get());
     }
 
     FloatSize size(page->frameHost().visualViewport().size());
     if (size != m_layer->size())
         m_layer->setSize(size);
 
     m_layer->setNeedsDisplay();
 }
 
 IntRect PageOverlay::computeInterestRect(const GraphicsLayer* graphicsLayer, const IntRect&) const
 {
     return IntRect(IntPoint(), expandedIntSize(m_layer->size()));
 }
 
 void PageOverlay::paintContents(const GraphicsLayer* graphicsLayer, GraphicsContext& gc, GraphicsLayerPaintingPhase phase, const IntRect& interestRect) const
 {
     ASSERT(m_layer);
     m_delegate->paintPageOverlay(*this, gc, interestRect.size());
 }
 
 String PageOverlay::debugName(const GraphicsLayer*) const
 {
     return "WebViewImpl Page Overlay Content Layer";
 }
 
 } // namespace blink