Try to cut down Browser/TabContents header dependencies.

chrome/common/extensions/extension.h

 // Copyright (c) 2010 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_COMMON_EXTENSIONS_EXTENSION_H_
 #define CHROME_COMMON_EXTENSIONS_EXTENSION_H_
 
 #include <map>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/file_path.h"
 #include "base/scoped_ptr.h"
 #include "base/values.h"
 #include "base/version.h"
 #include "chrome/common/extensions/extension_extent.h"
 #include "chrome/common/extensions/user_script.h"
 #include "chrome/common/extensions/url_pattern.h"
 #include "gfx/size.h"
 #include "googleurl/src/gurl.h"
 #include "testing/gtest/include/gtest/gtest_prod.h"
-#include "third_party/skia/include/core/SkBitmap.h"
 
 class ExtensionAction;
 class ExtensionResource;
+class SkBitmap;
 
 // Represents a Chrome extension.
 class Extension {
  public:
   typedef std::vector<URLPattern> URLPatternList;
   typedef std::map<const std::string, GURL> URLOverrideMap;
 
   // What an extension was loaded from.
   // NOTE: These values are stored as integers in the preferences, so you
   // really don't want to change any existing ones.
@@ skipping 563 matching lines @@
   scoped_ptr<DictionaryValue> extension_manifest;
   std::string extension_id;
   FilePath extension_path;
   Extension::Location extension_location;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ExtensionInfo);
 };
 
 #endif  // CHROME_COMMON_EXTENSIONS_EXTENSION_H_