Make RootScroller set the outer viewport scroll layer in the compositor

third_party/WebKit/Source/core/page/scrolling/RootScrollerController.h

Index: third_party/WebKit/Source/core/page/scrolling/RootScrollerController.h
diff --git a/third_party/WebKit/Source/core/page/scrolling/RootScrollerController.h b/third_party/WebKit/Source/core/page/scrolling/RootScrollerController.h
index dd49722681aa0d59b25106d491982c40fafad1b1..557102b0a67487c9d15718ca3c3ee79b1387e95e 100644
--- a/third_party/WebKit/Source/core/page/scrolling/RootScrollerController.h
+++ b/third_party/WebKit/Source/core/page/scrolling/RootScrollerController.h
@@ -12,6 +12,7 @@ namespace blink {
 
 class Document;
 class Element;
+class GraphicsLayer;
 class ViewportScrollCallback;
 
 // Manages the root scroller associated with a given document. The root scroller
@@ -70,6 +71,12 @@ public:
     // replaced by the defualt root scroller.
     void didUpdateLayout();
 
+    // This class needs to be informed of changes to compositing so that it can
+    // update the compositor when the effective root scroller changes.
+    void didUpdateCompositing();
+
+    GraphicsLayer* rootScrollerLayer();
+
     // TODO(bokan): Temporarily exposed to allow ScrollCustomization to
     // differentiate between real custom callback and the built-in viewport
     // apply scroll.