ui/gfx: Remove the deprecated "operator const GdkPixbuf*" from Image API.

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 102 matching lines @@
   SkBitmap* CopySkBitmap() const;
 #if defined(TOOLKIT_USES_GTK)
   GdkPixbuf* CopyGdkPixbuf() const;
 #elif defined(OS_MACOSX)
   NSImage* CopyNSImage() const;
 #endif
 
   // DEPRECATED ----------------------------------------------------------------
   // Conversion handlers. These wrap the ToType() variants.
   operator const SkBitmap&() const;
-#if defined(TOOLKIT_USES_GTK)
-  operator GdkPixbuf*() const;
-#elif defined(OS_MACOSX)
+#if defined(OS_MACOSX)
   operator NSImage*() const;
 #endif
   // ---------------------------------------------------------------------------
 
   // Gets the number of bitmaps in this image. This may cause a conversion
   // to a bitmap representation. Note, this function and GetSkBitmapAtIndex()
   // are primarily meant to be used by the theme provider.
   size_t GetNumberOfSkBitmaps() const;
 
   // Gets the bitmap at the given index. This may cause a conversion
@@ skipping 28 matching lines @@
   // be cheaply copied.
   scoped_refptr<internal::ImageStorage> storage_;
 
   friend class ::ImageTest;
   friend class ::ImageMacTest;
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_IMAGE_IMAGE_H_