Remove dead extensions tracking code.

extensions/common/extension_messages.h

 // Copyright 2014 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.
 
 // IPC messages for extensions.
 // Multiply-included message file, hence no include guard.
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 521 matching lines @@
 // Tell the render view to clear tab-specific permissions for some extensions.
 IPC_MESSAGE_CONTROL3(ExtensionMsg_ClearTabSpecificPermissions,
                      std::vector<std::string> /* extension_ids */,
                      bool /* update origin whitelist */,
                      int /* tab_id */)
 
 // Tell the renderer which type this view is.
 IPC_MESSAGE_ROUTED1(ExtensionMsg_NotifyRenderViewType,
                     extensions::ViewType /* view_type */)
 
-// Deliver a message sent with ExtensionHostMsg_PostMessage.
-IPC_MESSAGE_CONTROL1(ExtensionMsg_UsingWebRequestAPI,
-                     bool /* webrequest_used */)
-
 // The browser's response to the ExtensionMsg_WakeEventPage IPC.
 IPC_MESSAGE_CONTROL2(ExtensionMsg_WakeEventPageResponse,
                      int /* request_id */,
                      bool /* success */)
 
 // Ask the lazy background page if it is ready to be suspended. This is sent
 // when the page is considered idle. The renderer will reply with the same
 // sequence_id so that we can tell which message it is responding to.
 IPC_MESSAGE_CONTROL2(ExtensionMsg_ShouldSuspend,
                      std::string /* extension_id */,
@@ skipping 342 matching lines @@
                      int64_t /* service_worker_version_id */,
                      std::string /* request_uuid */)
 
 // Asks the browser to decrement the pending activity count for
 // the worker with version id |service_worker_version_id|.
 // |request_uuid| must match the GUID of a previous request, otherwise the
 // browser process ignores the IPC.
 IPC_MESSAGE_CONTROL2(ExtensionHostMsg_DecrementServiceWorkerActivity,
                      int64_t /* service_worker_version_id */,
                      std::string /* request_uuid */)