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

ui/events/blink/input_handler_proxy.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 <stddef.h>
 
 #include <algorithm>
 
@@ skipping 501 matching lines @@
         input_handler_->MouseUp();
       }
       return DID_NOT_HANDLE;
     }
     case WebInputEvent::kMouseMove: {
       const WebMouseEvent& mouse_event =
           static_cast<const WebMouseEvent&>(event);
       // TODO(davemoore): This should never happen, but bug #326635 showed some
       // surprising crashes.
       CHECK(input_handler_);
+      bool is_mouse_down =
+          mouse_event.button == blink::WebMouseEvent::Button::kLeft;
       input_handler_->MouseMoveAt(gfx::Point(mouse_event.PositionInWidget().x,
-                                             mouse_event.PositionInWidget().y));
+                                             mouse_event.PositionInWidget().y),
+                                  is_mouse_down);
       return DID_NOT_HANDLE;
     }
     case WebInputEvent::kMouseLeave: {
       CHECK(input_handler_);
       input_handler_->MouseLeave();
       return DID_NOT_HANDLE;
     }
 
     default:
       if (WebInputEvent::IsKeyboardEventType(event.GetType())) {
@@ skipping 1127 matching lines @@
                  scroll_elasticity_controller_->GetWeakPtr(), gesture_event,
                  scroll_result));
 }
 
 void InputHandlerProxy::SetTickClockForTesting(
     std::unique_ptr<base::TickClock> tick_clock) {
   tick_clock_ = std::move(tick_clock);
 }
 
 }  // namespace ui