Do not typedef ExtensionId/ID, since it's already available in extension_id.h

chrome/browser/extensions/api/messaging/message_service.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 CHROME_BROWSER_EXTENSIONS_API_MESSAGING_MESSAGE_SERVICE_H_
 #define CHROME_BROWSER_EXTENSIONS_API_MESSAGING_MESSAGE_SERVICE_H_
 
 #include <map>
 #include <memory>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/values.h"
 #include "chrome/browser/extensions/api/messaging/message_property_provider.h"
 #include "extensions/browser/api/messaging/native_message_host.h"
 #include "extensions/browser/browser_context_keyed_api_factory.h"
 #include "extensions/common/api/messaging/message.h"
+#include "extensions/common/extension_id.h"
 
 class GURL;
 class Profile;
 
 namespace content {
 class BrowserContext;
 }
 
 namespace extensions {
 class Extension;
@@ skipping 156 matching lines @@
   using MessageChannelMap = std::map<int, std::unique_ptr<MessageChannel>>;
 
   using PendingMessage = std::pair<int, Message>;
   using PendingMessagesQueue = std::vector<PendingMessage>;
   // A set of channel IDs waiting to complete opening, and any pending messages
   // queued to be sent on those channels.
   using PendingChannelMap = std::map<int, PendingMessagesQueue>;
 
   // A map of channel ID to information about the extension that is waiting
   // for that channel to open. Used for lazy background pages.
-  using ExtensionID = std::string;
   using PendingLazyBackgroundPageChannel =
-      std::pair<content::BrowserContext*, ExtensionID>;
+      std::pair<content::BrowserContext*, ExtensionId>;
   using PendingLazyBackgroundPageChannelMap =
       std::map<int, PendingLazyBackgroundPageChannel>;
 
   // Common implementation for opening a channel configured by |params|.
   //
   // |target_extension| will be non-null if |params->target_extension_id| is
   // non-empty, that is, if the target is an extension, it must exist.
   //
   // |did_enqueue| will be true if the channel opening was delayed while
   // waiting for an event page to start, false otherwise.
@@ skipping 105 matching lines @@
   LazyBackgroundTaskQueue* lazy_background_task_queue_;
 
   base::WeakPtrFactory<MessageService> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MessageService);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_MESSAGING_MESSAGE_SERVICE_H_