chrome: Cleanup class/struct forward declarations

chrome/browser/chromeos/input_method/mock_input_method_engine.h

 // Copyright 2014 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 CHROME_BROWSER_CHROMEOS_INPUT_METHOD_MOCK_INPUT_METHOD_ENGINE_H_
 #define CHROME_BROWSER_CHROMEOS_INPUT_METHOD_MOCK_INPUT_METHOD_ENGINE_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <string>
 #include <vector>
 
 #include "ui/base/ime/chromeos/input_method_descriptor.h"
 #include "ui/base/ime/ime_engine_handler_interface.h"
 
 namespace ui {
 class IMEEngineHandlerInterface;
 class KeyEvent;
 }  // namespace ui
 
 namespace chromeos {
 
-class CompositionText;
-
 class MockInputMethodEngine : public ui::IMEEngineHandlerInterface {
  public:
   MockInputMethodEngine();
   ~MockInputMethodEngine() override;
 
   // IMEEngineHandlerInterface overrides.
   const std::string& GetActiveComponentId() const override;
   bool ClearComposition(int context_id, std::string* error) override;
   bool CommitText(int context_id,
                   const char* text,
@@ skipping 33 matching lines @@
 
  private:
   std::string active_component_id_;
 
   std::string last_activated_property_;
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_INPUT_METHOD_MOCK_INPUT_METHOD_ENGINE_H_