Don't track mouse events in HWNDMessageHandler when they are forwarded by the LegacyRenderWidgetHost

ui/views/event_utils.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_VIEWS_EVENT_UTILS_H_
 #define UI_VIEWS_EVENT_UTILS_H_
 
 #include "ui/gfx/native_widget_types.h"
 #include "ui/views/views_export.h"
 
 namespace ui {
 class LocatedEvent;
 }
 
 namespace views {
 
 // Reposts a located event natively. Returns false when |event| could not be
 // reposted. |event| should be in screen coordinates. |window| is the target
 // window that the event will be forwarded to. Only some events are supported.
+// On Windows |window| can be NULL, in which case the event is forwarded to
+// the HWND at the current location if it is on the same thread.
 VIEWS_EXPORT bool RepostLocatedEvent(gfx::NativeWindow window,
                                      const ui::LocatedEvent& event);
 
 #if defined(OS_WIN)
 // Reposts a located event to the HWND passed in.
 VIEWS_EXPORT bool RepostLocatedEventWin(HWND window,
                                         const ui::LocatedEvent& event);
 #endif
 
 }  // namespace views
 
 #endif  // UI_VIEWS_EVENT_UTILS_H_