AcceleratorProvider: Make GetAcceleratorForCommandId const.

ui/base/accelerators/accelerator.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.
 
 // This class describe a keyboard accelerator (or keyboard shortcut).
 // Keyboard accelerators are registered with the FocusManager.
 // It has a copy constructor and assignment operator so that it can be copied.
 // It also defines the < operator so that it can be used as a key in a std::map.
 //
 
@@ skipping 100 matching lines @@
   virtual ~AcceleratorTarget() {}
 };
 
 // Since accelerator code is one of the few things that can't be cross platform
 // in the chrome UI, separate out just the GetAcceleratorForCommandId() from
 // the menu delegates.
 class AcceleratorProvider {
  public:
   // Gets the accelerator for the specified command id. Returns true if the
   // command id has a valid accelerator, false otherwise.
-  virtual bool GetAcceleratorForCommandId(int command_id,
-                                          ui::Accelerator* accelerator) = 0;
+  virtual bool GetAcceleratorForCommandId(
+      int command_id,
+      ui::Accelerator* accelerator) const = 0;
 
  protected:
   virtual ~AcceleratorProvider() {}
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_ACCELERATORS_ACCELERATOR_H_