[Extensions] Pull ExtensionId into its own file

extensions/common/extension.h

 // Copyright (c) 2013 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_EXTENSION_H_
 #define EXTENSIONS_COMMON_EXTENSION_H_
 
 #include <map>
 #include <memory>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "base/memory/linked_ptr.h"
 #include "base/memory/ref_counted.h"
 #include "base/threading/thread_checker.h"
+#include "extensions/common/extension_id.h"
 #include "extensions/common/extension_resource.h"
 #include "extensions/common/install_warning.h"
 #include "extensions/common/manifest.h"
 #include "extensions/common/url_pattern_set.h"
 #include "url/gurl.h"
 
 #if !defined(ENABLE_EXTENSIONS)
 #error "Extensions must be enabled"
 #endif
 
 namespace base {
 class DictionaryValue;
 class Version;
 }
 
 namespace extensions {
 class PermissionSet;
 class PermissionsData;
 class PermissionsParser;
 
-// Uniquely identifies an Extension, using 32 characters from the alphabet
-// 'a'-'p'.  An empty string represents "no extension".
-//
-// Note: If this gets used heavily in files that don't otherwise need to include
-// extension.h, we should pull it into a dedicated header.
-typedef std::string ExtensionId;
-
 // Represents a Chrome extension.
 // Once created, an Extension object is immutable, with the exception of its
 // RuntimeData. This makes it safe to use on any thread, since access to the
 // RuntimeData is protected by a lock.
 class Extension : public base::RefCountedThreadSafe<Extension> {
  public:
   enum State {
     DISABLED = 0,
     ENABLED,
     // An external extension that the user uninstalled. We should not reinstall
@@ skipping 506 matching lines @@
   const PermissionSet& permissions;
 
   UpdatedExtensionPermissionsInfo(const Extension* extension,
                                   const PermissionSet& permissions,
                                   Reason reason);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_COMMON_EXTENSION_H_