exo: Fix dragging edge cases

components/exo/wm_helper_ash.cc

 // Copyright 2016 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 "components/exo/wm_helper_ash.h"
 
 #include "ash/common/accessibility_delegate.h"
 #include "ash/common/wm/maximize_mode/maximize_mode_controller.h"
 #include "ash/common/wm_shell.h"
 #include "ash/display/display_manager.h"
@@ skipping 115 matching lines @@
 }
 
 void WMHelperAsh::OnMaximizeModeStarted() {
   NotifyMaximizeModeStarted();
 }
 
 void WMHelperAsh::OnMaximizeModeEnded() {
   NotifyMaximizeModeEnded();
 }
 
+void WMHelperAsh::OnOverviewModeStarting() {
+  NotifyOverviewModeStarted();
+}
+
+void WMHelperAsh::OnOverviewModeEnded() {
+  NotifyOverviewModeEnded();
+}
+
 }  // namespace exo