Don't set scroll client for main frame

Source/core/page/scrolling/ScrollingCoordinator.cpp

Index: Source/core/page/scrolling/ScrollingCoordinator.cpp
diff --git a/Source/core/page/scrolling/ScrollingCoordinator.cpp b/Source/core/page/scrolling/ScrollingCoordinator.cpp
index cd9e31fba2205fbb07a2894820a6b48d39c6a235..ae117773be2706396385ae016a77a1d7c9f846ad 100644
--- a/Source/core/page/scrolling/ScrollingCoordinator.cpp
+++ b/Source/core/page/scrolling/ScrollingCoordinator.cpp
@@ -240,7 +240,7 @@ void ScrollingCoordinator::scrollableAreaScrollbarLayerDidChange(ScrollableArea*
     if (!platformSupportsCoordinatedScrollbar)
         return;
 
-    bool isMainFrame = (scrollableArea == static_cast<ScrollableArea*>(m_page->mainFrame()->view()));
+    bool isMainFrame = isForMainFrame(scrollableArea);
     if (!isMainFrame && platformSupportsMainFrameOnly)
         return;
 
@@ -271,8 +271,10 @@ void ScrollingCoordinator::scrollableAreaScrollbarLayerDidChange(ScrollableArea*
 void ScrollingCoordinator::scrollableAreaScrollLayerDidChange(ScrollableArea* scrollableArea)
 {
     GraphicsLayer* scrollLayer = scrollLayerForScrollableArea(scrollableArea);
-    if (scrollLayer)
-        scrollLayer->setScrollableArea(scrollableArea);
+    if (scrollLayer) {
+        bool isMainFrame = isForMainFrame(scrollableArea);
+        scrollLayer->setScrollableArea(scrollableArea, isMainFrame);
+    }
 
     WebLayer* webLayer = scrollingWebLayerForScrollableArea(scrollableArea);
     if (webLayer) {
@@ -533,6 +535,11 @@ GraphicsLayer* ScrollingCoordinator::verticalScrollbarLayerForScrollableArea(Scr
     return scrollableArea->layerForVerticalScrollbar();
 }
 
+bool ScrollingCoordinator::isForMainFrame(ScrollableArea* scrollableArea) const
+{
+    return scrollableArea == m_page->mainFrame()->view();
+}
+
 GraphicsLayer* ScrollingCoordinator::scrollLayerForFrameView(FrameView* frameView)
 {
     Frame* frame = frameView->frame();