Moves WorkspaceEventHandler to ash/common

ash/common/wm_window.h

 // 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.
 
 #ifndef ASH_COMMON_WM_WINDOW_H_
 #define ASH_COMMON_WM_WINDOW_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 291 matching lines @@
 
   virtual void AddTransientWindowObserver(
       WmTransientWindowObserver* observer) = 0;
   virtual void RemoveTransientWindowObserver(
       WmTransientWindowObserver* observer) = 0;
 
   // Adds or removes a handler to receive events targeted at this window, before
   // this window handles the events itself; the handler does not recieve events
   // from embedded windows. This only supports windows with internal widgets;
   // see GetInternalWidget(). Ownership of the handler is not transferred.
+  //
+  // Also note that the target of these events is always an aura::Window.
   virtual void AddLimitedPreTargetHandler(ui::EventHandler* handler) = 0;
   virtual void RemoveLimitedPreTargetHandler(ui::EventHandler* handler) = 0;
 
  protected:
   virtual ~WmWindow() {}
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_WM_WINDOW_H_