Adding metrics logging for Simplified Gesture Navigation.

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 <memory>
 
 #include "base/macros.h"
@@ skipping 24 matching lines @@
   bool OnOverscrollUpdate(float delta_x, float delta_y) override;
   void OnOverscrollComplete(OverscrollMode overscroll_mode) override;
   void OnOverscrollModeChange(OverscrollMode old_mode,
                               OverscrollMode new_mode,
                               OverscrollSource source) override;
   base::Optional<float> GetMaxOverscrollDelta() const override;
 
   WebContentsImpl* web_contents_;
   std::unique_ptr<Affordance> affordance_;
   float completion_threshold_;
+  OverscrollSource source_ = OverscrollSource::NONE;
 
   // When an overscroll is active, represents the maximum overscroll delta we
   // expect in OnOverscrollUpdate().
   float max_delta_;
 
   DISALLOW_COPY_AND_ASSIGN(GestureNavSimple);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_WEB_CONTENTS_AURA_GESTURE_NAV_SIMPLE_H_