OverscrollController consumes scroll updates only during gesture-nav.

content/browser/web_contents/aura/gesture_nav_simple.h

Index: content/browser/web_contents/aura/gesture_nav_simple.h
diff --git a/content/browser/web_contents/aura/gesture_nav_simple.h b/content/browser/web_contents/aura/gesture_nav_simple.h
index e8466e5e6e24fe3377cb72b767d8f55826a59d73..eeecebf3cb9fff187bec3b6cbf633db4ebd8d05c 100644
--- a/content/browser/web_contents/aura/gesture_nav_simple.h
+++ b/content/browser/web_contents/aura/gesture_nav_simple.h
@@ -32,11 +32,12 @@ class GestureNavSimple : public OverscrollControllerDelegate {
   void ApplyEffectsAndDestroy(const gfx::Transform& transform, float opacity);
   void AbortGestureAnimation();
   void CompleteGestureAnimation();
-  void ApplyEffectsForDelta(float delta_x);
+  bool ApplyEffectsForDelta(float delta_x);
 
   // OverscrollControllerDelegate:
   virtual gfx::Rect GetVisibleBounds() const OVERRIDE;
-  virtual void OnOverscrollUpdate(float delta_x, float delta_y) OVERRIDE;
+  // Returns true if the scroll update was consumed.
+  virtual bool OnOverscrollUpdate(float delta_x, float delta_y) OVERRIDE;
   virtual void OnOverscrollComplete(OverscrollMode overscroll_mode) OVERRIDE;
   virtual void OnOverscrollModeChange(OverscrollMode old_mode,
                                       OverscrollMode new_mode) OVERRIDE;