[RootLayerScrolls] Fix frame scrolling layer in ScrollingCoordinator

third_party/WebKit/Source/platform/scroll/ScrollableArea.h

Index: third_party/WebKit/Source/platform/scroll/ScrollableArea.h
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollableArea.h b/third_party/WebKit/Source/platform/scroll/ScrollableArea.h
index 4df2ffb0bfe153c7fc401710cabc6afbd4c38a90..bfb1eb9e89a48809f243273475c67b1a9a646be8 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollableArea.h
+++ b/third_party/WebKit/Source/platform/scroll/ScrollableArea.h
@@ -322,6 +322,8 @@ class PLATFORM_EXPORT ScrollableArea : public GarbageCollectedMixin {
     return ScrollBehaviorInstant;
   }
 
+  virtual bool isScrollable() const { return true; }
+
   // TODO(bokan): FrameView::setScrollOffset uses updateScrollbars to scroll
   // which bails out early if its already in updateScrollbars, the effect being
   // that programmatic scrolls (i.e. setScrollOffset) are disabled when in