Ensure that if FrameView::isScrollable() is false, the assoc WebLayer is, too.

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 a1b1ee214807db01d3a9195c435bbbd7937d4147..372669a22ddc35c6152b0f043a545cbe1585eefe 100644
--- a/Source/core/page/scrolling/ScrollingCoordinator.cpp
+++ b/Source/core/page/scrolling/ScrollingCoordinator.cpp
@@ -152,11 +152,10 @@ void ScrollingCoordinator::updateAfterCompositingChange()
         m_touchEventTargetRectsAreDirty = false;
     }
 
-    FrameView* frameView = m_page->mainFrame()->view();
-    bool frameIsScrollable = frameView && frameView->isScrollable();
-    if (m_wasFrameScrollable != frameIsScrollable)
+    if (frameViewIsScrollableIsDirty())
         updateShouldUpdateScrollLayerPositionOnMainThread();
-    m_wasFrameScrollable = frameIsScrollable;
+
+    updateMainFrameIsScrollable();
 
     const FrameTree& tree = m_page->mainFrame()->tree();
     for (const Frame* child = tree.firstChild(); child; child = child->tree().nextSibling()) {
@@ -929,4 +928,17 @@ bool ScrollingCoordinator::frameViewIsScrollableIsDirty() const
     return frameIsScrollable != m_wasFrameScrollable;
 }
 
+void ScrollingCoordinator::updateMainFrameIsScrollable()
+{
+    FrameView* frameView = m_page->mainFrame()->view();
+    bool frameIsScrollable = frameView && frameView->isScrollable();
+    m_wasFrameScrollable = frameIsScrollable;
+
+    if (!frameView)
+        return;
+
+    if (WebLayer* scrollingWebLayer = scrollingWebLayerForScrollableArea(frameView))
+        scrollingWebLayer->setScrollable(frameIsScrollable);
+}
+
 } // namespace WebCore