[Android] Add slack to allow refresh after overscrolling

content/browser/android/overscroll_glow.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_ANDROID_OVERSCROLL_GLOW_H_
 #define CONTENT_BROWSER_ANDROID_OVERSCROLL_GLOW_H_
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/time/time.h"
@@ skipping 51 matching lines @@
   void UpdateDisplay(const gfx::SizeF& viewport_size,
                      const gfx::SizeF& content_size,
                      const gfx::Vector2dF& content_scroll_offset);
 
   // Reset the effect to its inactive state, clearing any active effects.
   void Reset();
 
   // Whether the effect is active, either being pulled or receding.
   bool IsActive() const;
 
+  // The maximum alpha value (in the range [0,1]) of any animated edge layers.
+  // If the effect is inactive, this will be 0.
+  float GetVisibleAlpha() const;
+
  private:
   enum Axis { AXIS_X, AXIS_Y };
 
   // Returns whether the effect has been properly initialized.
   bool InitializeIfNecessary();
   bool CheckNeedsAnimate();
   void UpdateLayerAttachment(cc::Layer* parent);
   void Detach();
   void Pull(base::TimeTicks current_time,
             const gfx::Vector2dF& overscroll_delta,
@@ skipping 14 matching lines @@
   bool initialized_;
 
   scoped_refptr<cc::Layer> root_layer_;
 
   DISALLOW_COPY_AND_ASSIGN(OverscrollGlow);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_ANDROID_OVERSCROLL_GLOW_H_