Fix the bug of multiple overlays.

ash/wm/overlay_event_filter.cc

 // Copyright (c) 2012 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 "ash/wm/overlay_event_filter.h"
 
 #include "ash/wm/partial_screenshot_view.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_delegate.h"
 #include "ui/events/event.h"
@@ skipping 38 matching lines @@
 
 void OverlayEventFilter::OnAppTerminating() {
   Cancel();
 }
 
 void OverlayEventFilter::OnLockStateChanged(bool locked) {
   Cancel();
 }
 
 void OverlayEventFilter::Activate(Delegate* delegate) {
+  if (delegate_)
+    delegate_->Cancel();
   delegate_ = delegate;
 }
 
-void OverlayEventFilter::Deactivate() {
-  delegate_ = NULL;
+void OverlayEventFilter::Deactivate(Delegate* delegate) {
+  if (delegate_ == delegate)
+    delegate_ = NULL;
 }
 
 void OverlayEventFilter::Cancel() {
   if (delegate_)
     delegate_->Cancel();
 }
 
+bool OverlayEventFilter::IsActive() {
+  return delegate_;
+}
+
 }  // namespace ash