Delegate root layer scroll offset to android_webview.

content/public/browser/android/synchronous_compositor.h

Index: content/public/browser/android/synchronous_compositor.h
diff --git a/content/public/browser/android/synchronous_compositor.h b/content/public/browser/android/synchronous_compositor.h
index f380b0e3e5f43063383f3ddbc67152764ffbc7a0..0fb2290c557c049adc45eb0873df927fda98eb5c 100644
--- a/content/public/browser/android/synchronous_compositor.h
+++ b/content/public/browser/android/synchronous_compositor.h
@@ -51,6 +51,11 @@ class SynchronousCompositor {
       const gfx::Transform& transform,
       gfx::Rect damage_area) = 0;
 
+  // Should be called by the embedder after the embedder had modified the
+  // scroll offset of the root layer (as returned by
+  // SynchronousCompositorClient::GetTotalRootLayerScrollOffset).
+  virtual void DidChangeRootLayerScrollOffset() = 0;
+
  protected:
   virtual ~SynchronousCompositor() {}
 };