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

ui/events/blink/input_handler_proxy_unittest.cc

 // 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.
 
 #include "ui/events/blink/input_handler_proxy.h"
 
 #include <memory>
 
 #include "base/macros.h"
 #include "base/test/histogram_tester.h"
@@ skipping 203 matching lines @@
     return new FakeWebGestureCurve(
         blink::WebFloatSize(velocity.x, velocity.y),
         blink::WebFloatSize(cumulative_scroll.width, cumulative_scroll.height));
   }
 
   MOCK_METHOD4(DidOverscroll,
                void(const gfx::Vector2dF& accumulated_overscroll,
                     const gfx::Vector2dF& latest_overscroll_delta,
                     const gfx::Vector2dF& current_fling_velocity,
                     const gfx::PointF& causal_event_viewport_point));
+  void DidStartFlinging() override {}
   void DidStopFlinging() override {}
   void DidAnimateForInput() override {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(MockInputHandlerProxyClient);
 };
 
 class MockInputHandlerProxyClientWithDidAnimateForInput
     : public MockInputHandlerProxyClient {
  public:
@@ skipping 2624 matching lines @@
       testing::ElementsAre(base::Bucket(1, 1), base::Bucket(3, 1),
                            base::Bucket(5, 1), base::Bucket(14, 1)));
 }
 
 
 INSTANTIATE_TEST_CASE_P(AnimateInput,
                         InputHandlerProxyTest,
                         testing::ValuesIn(test_types));
 }  // namespace test
 }  // namespace ui