Remove forward declarations of unused ImageRepGdk and ImageRepCairo

ui/gfx/image/image.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.
 
 // An Image wraps an image any flavor, be it platform-native GdkBitmap/NSImage,
 // or a SkBitmap. This also provides easy conversion to other image types
 // through operator overloading. It will cache the converted representations
 // internally to prevent double-conversion.
 //
 // The lifetime of both the initial representation and any converted ones are
@@ skipping 34 matching lines @@
 class Size;
 
 namespace internal {
 class ImageRep;
 class ImageStorage;
 }
 
 class GFX_EXPORT Image {
  public:
   enum RepresentationType {
-    kImageRepGdk,
     kImageRepCocoa,
     kImageRepCocoaTouch,
-    kImageRepCairo,
     kImageRepSkia,
     kImageRepPNG,
   };
 
   typedef std::map<RepresentationType, internal::ImageRep*> RepresentationMap;
 
   // Creates an empty image with no representations.
   Image();
 
   // Creates a new image by copying the raw PNG-encoded input for use as the
@@ skipping 125 matching lines @@
   // be cheaply copied.
   scoped_refptr<internal::ImageStorage> storage_;
 
   friend class ::ImageTest;
   friend class ::ImageMacTest;
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_IMAGE_IMAGE_H_