OverscrollController consumes scroll updates only during gesture-nav.

content/browser/web_contents/web_contents_view_aura.h

 // Copyright (c) 2012 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_WEB_CONTENTS_VIEW_AURA_H_
 #define CONTENT_BROWSER_WEB_CONTENTS_WEB_CONTENTS_VIEW_AURA_H_
 
 #include <vector>
 
 #include "base/memory/ref_counted.h"
@@ skipping 121 matching lines @@
                              blink::WebDragOperationsMask operations,
                              const gfx::ImageSkia& image,
                              const gfx::Vector2d& image_offset,
                              const DragEventSourceInfo& event_info) OVERRIDE;
   virtual void UpdateDragCursor(blink::WebDragOperation operation) OVERRIDE;
   virtual void GotFocus() OVERRIDE;
   virtual void TakeFocus(bool reverse) OVERRIDE;
 
   // Overridden from 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;
 
   // Overridden from ui::ImplicitAnimationObserver:
   virtual void OnImplicitAnimationsCompleted() OVERRIDE;
 
   // Overridden from aura::WindowDelegate:
   virtual gfx::Size GetMinimumSize() const OVERRIDE;
   virtual gfx::Size GetMaximumSize() const OVERRIDE;
@@ skipping 79 matching lines @@
   // On Windows we can run into problems if resources get released within the
   // initialization phase while the content (and its dimensions) are not known.
   bool is_or_was_visible_;
 
   DISALLOW_COPY_AND_ASSIGN(WebContentsViewAura);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_WEB_CONTENTS_WEB_CONTENTS_VIEW_AURA_H_