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..fd5d0badcaaedc72b455799e3acfa39a09c4c8d9 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 == static_cast<ScrollableArea*>(m_page->mainFrame()->view());

[jamesr, 2013/07/04 00:37:37]

do you need the static cast on the RHS of this for the comparison to compile?
the compiler knows the types on each side so it should be able to do the
mangling necessary (which should only be offset adjustments in case of multiple
inheritance, which we don't have here).

[enne (OOO), 2013/07/04 00:50:17]

You're right.  The compiler will do the right thing here.  Done.

+}
+
 GraphicsLayer* ScrollingCoordinator::scrollLayerForFrameView(FrameView* frameView)
 {
     Frame* frame = frameView->frame();