Add UMA metric for tracking listeners for blocking touch while fling is happening

ui/events/blink/input_handler_proxy.h

 // Copyright 2013 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 UI_EVENTS_BLINK_INPUT_HANDLER_PROXY_H_
 #define UI_EVENTS_BLINK_INPUT_HANDLER_PROXY_H_
 
 #include <memory>
 
 #include "base/containers/hash_tables.h"
@@ skipping 74 matching lines @@
                            const gfx::Point& anchor) override;
 
   // blink::WebGestureCurveTarget implementation.
   bool scrollBy(const blink::WebFloatSize& offset,
                 const blink::WebFloatSize& velocity) override;
 
   bool gesture_scroll_on_impl_thread_for_testing() const {
     return gesture_scroll_on_impl_thread_;
   }
 
+  bool isFlinging() const {
+    return (!!fling_curve_) || fling_may_be_active_on_main_thread_;
+  }
+
  protected:
   void RecordMainThreadScrollingReasons(blink::WebInputEvent::Type type,
                                         uint32_t reasons);
 
  private:
   friend class test::InputHandlerProxyTest;
 
   // Helper functions for handling more complicated input events.
   EventDisposition HandleMouseWheel(
       const blink::WebMouseWheelEvent& event);
@@ skipping 107 matching lines @@
   int32_t touch_start_result_;
 
   base::TimeTicks last_fling_animate_time_;
 
   DISALLOW_COPY_AND_ASSIGN(InputHandlerProxy);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_BLINK_INPUT_HANDLER_PROXY_H_