Keep expanded if mouse moves off of scrollbar while dragging

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 119 matching lines @@
   bool GetScrollOffsetForLayer(int layer_id,
                                gfx::ScrollOffset* offset) override {
     return false;
   }
   bool ScrollLayerTo(int layer_id, const gfx::ScrollOffset& offset) override {
     return false;
   }
 
   void BindToClient(cc::InputHandlerClient* client) override {}
 
+  void MouseDownAt(const gfx::Point& viewport_point) override {}
+  void MouseUp() override {}
+
   void MouseMoveAt(const gfx::Point& mouse_position) 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(DoTouchEventsBlockScrollAt, bool(const gfx::Point& point));
@@ skipping 2653 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