beginSmoothScroll should send wheel ticks at constant velocity.

content/browser/renderer_host/render_widget_host_impl.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_RENDERER_HOST_RENDER_WIDGET_HOST_IMPL_H_
 #define CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_IMPL_H_
 
 #include <deque>
 #include <map>
 #include <queue>
 #include <string>
 #include <vector>
 
 #include "base/callback.h"
 #include "base/gtest_prod_util.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/process_util.h"
 #include "base/string16.h"
+#include "base/time.h"
 #include "base/timer.h"
 #include "build/build_config.h"
 #include "content/common/view_message_enums.h"
 #include "content/public/browser/render_widget_host.h"
 #include "content/public/common/page_zoom.h"
 #include "ui/base/ime/text_input_type.h"
 #include "ui/gfx/native_widget_types.h"
 
 class MockRenderWidgetHost;
 class WebCursor;
@@ skipping 786 matching lines @@
   // Keeps track of whether the webpage has any touch event handler. If it does,
   // then touch events are sent to the renderer. Otherwise, the touch events are
   // not sent to the renderer.
   bool has_touch_handler_;
 
   base::WeakPtrFactory<RenderWidgetHostImpl> weak_factory_;
 
   typedef std::map<int, scoped_refptr<SmoothScrollGesture> >
       SmoothScrollGestureMap;
   SmoothScrollGestureMap active_smooth_scroll_gestures_;
+  base::TimeTicks last_smooth_scroll_gestures_tick_time_;
+  bool tick_active_smooth_scroll_gestures_task_posted_;
 
   scoped_ptr<GestureEventFilter> gesture_event_filter_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_IMPL_H_