OverscrollController consumes scroll updates only during gesture-nav.

content/browser/renderer_host/overscroll_controller_delegate.h

Index: content/browser/renderer_host/overscroll_controller_delegate.h
diff --git a/content/browser/renderer_host/overscroll_controller_delegate.h b/content/browser/renderer_host/overscroll_controller_delegate.h
index 59295ce41277247a8ef7896087e2408f5c0f523c..54b5da18857277eb816916d9305b76738b185f44 100644
--- a/content/browser/renderer_host/overscroll_controller_delegate.h
+++ b/content/browser/renderer_host/overscroll_controller_delegate.h
@@ -23,8 +23,9 @@ class OverscrollControllerDelegate {
   // events will only be processed if the visible bounds are non-empty.
   virtual gfx::Rect GetVisibleBounds() const = 0;
 
-  // This is called for each update in the overscroll amount.
-  virtual void OnOverscrollUpdate(float delta_x, float delta_y) = 0;
+  // This is called for each update in the overscroll amount. Returns true if
+  // the delegate consumed the event.
+  virtual bool OnOverscrollUpdate(float delta_x, float delta_y) = 0;
 
   // This is called when the overscroll completes.
   virtual void OnOverscrollComplete(OverscrollMode overscroll_mode) = 0;