Added comments in the WindowEventDispatcher::OnOtherRootGotCapture function.

ui/aura/window_event_dispatcher.cc

 // Copyright 2014 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/aura/window_event_dispatcher.h"
 
 #include "base/bind.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
@@ skipping 373 matching lines @@
   } else {
     // Make sure mouse_moved_handler gets updated.
     DispatchDetails details = SynthesizeMouseMoveEvent();
     if (details.dispatcher_destroyed)
       return;
   }
   mouse_pressed_handler_ = NULL;
 }
 
 void WindowEventDispatcher::OnOtherRootGotCapture() {
-  // Sending the mouse exit causes bugs on Windows (e.g. crbug.com/394672).
-  // TODO(pkotwicz): Fix the bugs and send mouse exit on Windows too.
+  // Windows provides the TrackMouseEvents API which allows us to rely on the
+  // OS to send us the mouse exit events (WM_MOUSELEAVE). Additionally on
+  // desktop Windows, every top level window could potentially have its own
+  // root window, in which case this function will get called whenever those
+  // windows grab mouse capture. Sending mouse exit messages in these cases
+  // causes subtle bugs like (crbug.com/394672).
 #if !defined(OS_WIN)
   if (mouse_moved_handler_) {
     // Dispatch a mouse exit to reset any state associated with hover. This is
     // important when going from no window having capture to a window having
     // capture because we do not dispatch ET_MOUSE_CAPTURE_CHANGED in this case.
     DispatchDetails details = DispatchMouseExitAtPoint(
         GetLastMouseLocationInRoot());
     if (details.dispatcher_destroyed)
       return;
   }
@@ skipping 485 matching lines @@
     if (!ui::GestureRecognizer::Get()->ProcessTouchEventPreDispatch(orig_event,
                                                                     target)) {
       event->SetHandled();
     }
   }
 
   PreDispatchLocatedEvent(target, event);
 }
 
 }  // namespace aura