chrome: Cleanup class/struct forward declarations

chrome/browser/ui/ime/ime_native_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 CHROME_BROWSER_UI_IME_IME_NATIVE_WINDOW_H_
 #define CHROME_BROWSER_UI_IME_IME_NATIVE_WINDOW_H_
 
-namespace content {
-class WebContents;
-}
-
 namespace gfx {
 class Rect;
 }
 
 namespace ui {
 
 // The interface to bridge the interactions between ImeWindow and ImeWindowView.
 // Note that c/b/ui cannot depend upon the platform specific implementations.
 // This is held weakly by ImeWindow. The subclass should do self-destruction
 // while the IME window (widget) is destroyed, and its destructor is expected
@@ skipping 21 matching lines @@
   // For testing.
   virtual bool IsVisible() const = 0;
 
  protected:
   virtual ~ImeNativeWindow() {}
 };
 
 }  // namespace ui
 
 #endif  // CHROME_BROWSER_UI_IME_IME_NATIVE_WINDOW_H_