beginSmoothScroll should send wheel ticks at constant velocity.

content/browser/renderer_host/render_widget_host_impl.h

Index: content/browser/renderer_host/render_widget_host_impl.h
diff --git a/content/browser/renderer_host/render_widget_host_impl.h b/content/browser/renderer_host/render_widget_host_impl.h
index 3529de68e65298e5d04bc1d1d769111898b6421d..b544b93fbe1274dd12b521ab0f758a1bf4a7de7f 100644
--- a/content/browser/renderer_host/render_widget_host_impl.h
+++ b/content/browser/renderer_host/render_widget_host_impl.h
@@ -17,6 +17,7 @@
 #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"
@@ -825,6 +826,8 @@ class CONTENT_EXPORT RenderWidgetHostImpl : virtual public RenderWidgetHost,
   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_;