Made layout viewport scroll updates from compositor work like ordinary layers.

third_party/WebKit/Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 53 matching lines @@
 #include "core/layout/ScrollAlignment.h"
 #include "core/layout/TextAutosizer.h"
 #include "core/layout/TracedLayoutObject.h"
 #include "core/layout/api/LayoutBoxModel.h"
 #include "core/layout/api/LayoutItem.h"
 #include "core/layout/api/LayoutViewItem.h"
 #include "core/layout/compositing/CompositedLayerMapping.h"
 #include "core/layout/compositing/CompositedSelection.h"
 #include "core/layout/compositing/PaintLayerCompositor.h"
 #include "core/layout/svg/LayoutSVGRoot.h"
+#include "core/loader/DocumentLoader.h"
 #include "core/loader/FrameLoader.h"
 #include "core/loader/FrameLoaderClient.h"
 #include "core/page/AutoscrollController.h"
 #include "core/page/ChromeClient.h"
 #include "core/page/FocusController.h"
 #include "core/page/FrameTree.h"
 #include "core/page/Page.h"
 #include "core/page/scrolling/ChildViewportScrollCallback.h"
 #include "core/page/scrolling/RootScrollerController.h"
 #include "core/page/scrolling/RootViewportScrollCallback.h"
@@ skipping 3318 matching lines @@
     if (m_didScrollTimer.isActive())
         m_didScrollTimer.stop();
     m_didScrollTimer.startOneShot(resourcePriorityUpdateDelayAfterScroll, BLINK_FROM_HERE);
 
     if (AXObjectCache* cache = m_frame->document()->existingAXObjectCache())
         cache->handleScrollPositionChanged(this);
 
     frame().loader().saveScrollState();
     frame().loader().client()->didChangeScrollOffset();
 
+    if (scrollType == CompositorScroll && m_frame->isMainFrame()) {
+        if (DocumentLoader* documentLoader = m_frame->loader().documentLoader())
+            documentLoader->initialScrollState().wasScrolledByUser = true;
+    }
+
     if (scrollType != AnchoringScroll)
         clearScrollAnchor();
 }
 
 void FrameView::clearScrollAnchor()
 {
     if (!RuntimeEnabledFeatures::scrollAnchoringEnabled())
         return;
     m_scrollAnchor.clear();
 }
@@ skipping 853 matching lines @@
 }
 
 bool FrameView::canThrottleRendering() const
 {
     if (!RuntimeEnabledFeatures::renderingPipelineThrottlingEnabled())
         return false;
     return m_subtreeThrottled || (m_hiddenForThrottling && m_crossOriginForThrottling);
 }
 
 } // namespace blink