Move CrxFile, FileReader, ExtensionResource to src/extensions.

extensions/common/constants.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.
 
 #ifndef EXTENSIONS_COMMON_CONSTANTS_H_
 #define EXTENSIONS_COMMON_CONSTANTS_H_
 
+#include "base/files/file_path.h"
+
 namespace extensions {
 
 // Scheme we serve extension content from.
 extern const char kExtensionScheme[];
 
+  // The name of the manifest inside an extension.
+extern const base::FilePath::CharType kManifestFilename[];
+
+  // The name of locale folder inside an extension.
+extern const base::FilePath::CharType kLocaleFolder[];
+
+  // The name of the messages file inside an extension.
+extern const base::FilePath::CharType kMessagesFilename[];
+
+// The base directory for subdirectories with platform-specific code.
+extern const base::FilePath::CharType kPlatformSpecificFolder[];
+
 }  // namespace extensions
 
 #endif  // EXTENSIONS_COMMON_CONSTANTS_H_