Added comments in the WindowEventDispatcher::OnOtherRootGotCapture function.

ui/aura/window_event_dispatcher.cc

Index: ui/aura/window_event_dispatcher.cc
diff --git a/ui/aura/window_event_dispatcher.cc b/ui/aura/window_event_dispatcher.cc
index eb08269c95bc94138074385699a928d294916208..e100bc82bdf810db4cb4f4c54445cea0a408144b 100644
--- a/ui/aura/window_event_dispatcher.cc
+++ b/ui/aura/window_event_dispatcher.cc
@@ -391,8 +391,12 @@ void WindowEventDispatcher::UpdateCapture(Window* old_capture,
 }
 
 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