OverscrollController consumes scroll updates only during gesture-nav.

content/browser/web_contents/aura/gesture_nav_simple.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_WEB_CONTENTS_AURA_GESTURE_NAV_SIMPLE_H_
 #define CONTENT_BROWSER_WEB_CONTENTS_AURA_GESTURE_NAV_SIMPLE_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "content/browser/renderer_host/overscroll_controller_delegate.h"
 
@@ skipping 14 matching lines @@
 // of the web-contents as a hint for pending navigations from overscroll.
 class GestureNavSimple : public OverscrollControllerDelegate {
  public:
   explicit GestureNavSimple(WebContentsImpl* web_contents);
   virtual ~GestureNavSimple();
 
  private:
   void ApplyEffectsAndDestroy(const gfx::Transform& transform, float opacity);
   void AbortGestureAnimation();
   void CompleteGestureAnimation();
-  void ApplyEffectsForDelta(float delta_x);
+  // Returns true if the delta was applied.
+  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;
 
   WebContentsImpl* web_contents_;
   scoped_ptr<ui::Layer> clip_layer_;
   scoped_ptr<ui::Layer> arrow_;
   scoped_ptr<ArrowLayerDelegate> arrow_delegate_;
   float completion_threshold_;
 
   DISALLOW_COPY_AND_ASSIGN(GestureNavSimple);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_WEB_CONTENTS_AURA_GESTURE_NAV_SIMPLE_H_