Do not consume Alt-Shift-Up event for IME switch.

ash/ime_control_delegate.h

 // 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.
 
 #ifndef ASH_IME_CONTROL_DELEGATE_H_
 #define ASH_IME_CONTROL_DELEGATE_H_
 
 namespace ui {
 class Accelerator;
 }  // namespace ui
 
 namespace ash {
 
 // Delegate for controlling IME (input method editor).
 class ImeControlDelegate {
  public:
   virtual ~ImeControlDelegate() {}
 
-  virtual bool HandleNextIme() = 0;
+  // Changes the IME to what is listed next. This function do nothing if there
+  // is only one IME is enabled.
+  virtual void HandleNextIme() = 0;
+
+  // Changes the IME to previously selected one. If there is no previously
+  // selected IMEs, chooses the next listed IME. This function returns false if
+  // there is only one IME is enabled.
   virtual bool HandlePreviousIme(const ui::Accelerator& accelerator) = 0;
+
   // Switches to another IME depending on the |accelerator|.
   virtual bool HandleSwitchIme(const ui::Accelerator& accelerator) = 0;
 
   // Checks for special language anomalies and re-map the |accelerator|
   // accordingly.
   virtual ui::Accelerator RemapAccelerator(
       const ui::Accelerator& accelerator) = 0;
 };
 
 }  // namespace ash
 
 #endif  // ASH_IME_CONTROL_DELEGATE_H_