extensions: Cleanup class/struct fwd declarations

extensions/browser/extension_icon_placeholder.h

 // Copyright 2015 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 EXTENSIONS_BROWSER_EXTENSION_ICON_PLACEHOLDER_H_
 #define EXTENSIONS_BROWSER_EXTENSION_ICON_PLACEHOLDER_H_
 
 #include <string>
 
 #include "base/macros.h"
 #include "base/strings/string16.h"
 #include "extensions/common/constants.h"
 #include "ui/gfx/image/canvas_image_source.h"
 #include "ui/gfx/image/image.h"
 
 namespace gfx {
 class Canvas;
-class Size;
 }
 
 namespace extensions {
 
 // An extension icon image with a gray background and the first letter of the
 // extension name, so that not all extensions without an icon look the same.
 class ExtensionIconPlaceholder : public gfx::CanvasImageSource {
  public:
   ExtensionIconPlaceholder(extension_misc::ExtensionIcons size,
                            const std::string& name);
@@ skipping 16 matching lines @@
 
   // The gray background image, on top of which the letter is drawn.
   gfx::Image base_image_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionIconPlaceholder);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_EXTENSION_ICON_PLACEHOLDER_H_