Don't fade in overlay scrollbar when user interacting the content under scrollbar.

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/bind.h"
 #include "base/macros.h"
@@ skipping 189 matching lines @@
     return false;
   }
 
   void BindToClient(cc::InputHandlerClient* client,
                     bool touchpad_and_wheel_scroll_latching_enabled) override {}
 
   void MouseDown() override {}
   void MouseUp() override {}
   void MouseLeave() override {}
 
-  void MouseMoveAt(const gfx::Point& mouse_position) override {}
+  void MouseMoveAt(const gfx::Point& mouse_position,
+                   bool is_mouse_down) override {}
 
   MOCK_CONST_METHOD2(IsCurrentlyScrollingLayerAt,
                      bool(const gfx::Point& point,
                           cc::InputHandler::ScrollInputType type));
 
   MOCK_CONST_METHOD1(
       GetEventListenerProperties,
       cc::EventListenerProperties(cc::EventListenerClass event_class));
   MOCK_METHOD1(EventListenerTypeForTouchStartOrMoveAt,
                cc::InputHandler::TouchStartOrMoveEventListenerType(
@@ skipping 3689 matching lines @@
 INSTANTIATE_TEST_CASE_P(AnimateInput,
                         InputHandlerProxyWithoutWheelScrollLatchingTest,
                         testing::ValuesIn(test_types));
 
 INSTANTIATE_TEST_CASE_P(InputHandlerProxyEventQueueTests,
                         InputHandlerProxyEventQueueTest,
                         testing::Bool());
 
 }  // namespace test
 }  // namespace ui