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

third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp

Index: third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
diff --git a/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp b/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
index 6454137452f1d4280f9507e3ef0b6eb625ea4745..8a3ec64fa580ec7a2f78725cd2d0609849ace50d 100644
--- a/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
+++ b/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
@@ -386,8 +386,11 @@ bool ScrollingCoordinator::scrollableAreaScrollLayerDidChange(ScrollableArea* sc
 
     GraphicsLayer* scrollLayer = scrollableArea->layerForScrolling();
 
-    if (scrollLayer)
-        scrollLayer->setScrollableArea(scrollableArea, isForViewport(scrollableArea));
+    if (scrollLayer) {
+        bool isForVisualViewport =
+            scrollableArea == &m_page->frameHost().visualViewport();
+        scrollLayer->setScrollableArea(scrollableArea, isForVisualViewport);
+    }
 
     WebLayer* webLayer = toWebLayer(scrollableArea->layerForScrolling());
     WebLayer* containerLayer = toWebLayer(scrollableArea->layerForContainer());
@@ -934,15 +937,6 @@ bool ScrollingCoordinator::isForMainFrame(ScrollableArea* scrollableArea) const
     return scrollableArea == m_page->deprecatedLocalMainFrame()->view();
 }
 
-bool ScrollingCoordinator::isForViewport(ScrollableArea* scrollableArea) const
-{
-    bool isForOuterViewport = m_page->settings().rootLayerScrolls() ?
-        isForRootLayer(scrollableArea) :
-        isForMainFrame(scrollableArea);
-
-    return isForOuterViewport || scrollableArea == &m_page->frameHost().visualViewport();
-}
-
 void ScrollingCoordinator::frameViewRootLayerDidChange(FrameView* frameView)
 {
     ASSERT(isMainThread());