Fix build break on linux (compiler warning).

chrome/browser/extensions/extension.h

 // Copyright (c) 2006-2008 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_EXTENSIONS_EXTENSION_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 47 matching lines @@
   static const char* kInvalidMatchCountError;
   static const char* kInvalidMatchError;
   static const char* kInvalidMatchesError;
   static const char* kInvalidNameError;
   static const char* kInvalidRunAtError;
   static const char* kInvalidVersionError;
   static const char* kInvalidZipHashError;
   static const char* kInvalidPluginsDirError;
 
   // The number of bytes in a legal id.
-  static const int kIdSize;
+  static const size_t kIdSize;
 
   // Creates an absolute url to a resource inside an extension. The
   // |extension_url| argument should be the url() from an Extension object. The
   // |relative_path| can be untrusted user input. The returned URL will either
   // be invalid() or a child of |extension_url|.
   // NOTE: Static so that it can be used from multiple threads.
   static GURL GetResourceURL(const GURL& extension_url,
                              const std::string& relative_path);
 
   // Creates an absolute path to a resource inside an extension. The
@@ skipping 70 matching lines @@
 
   // A SHA1 hash of the contents of the zip file.  Note that this key is only
   // present in the manifest that's prepended to the zip.  The inner manifest
   // will not have this key.
   std::string zip_hash_;
 
   DISALLOW_COPY_AND_ASSIGN(Extension);
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_H_