[Extensions] Make port creation synchronous in unload handlers

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 667 matching lines @@
 // Open a channel to all listening contexts owned by the extension with
 // the given ID. This responds asynchronously with ExtensionMsg_AssignPortId.
 // If an error occurred, the opener will be notified asynchronously.
 IPC_MESSAGE_CONTROL5(ExtensionHostMsg_OpenChannelToExtension,
                      int /* frame_routing_id */,
                      ExtensionMsg_ExternalConnectionInfo,
                      std::string /* channel_name */,
                      bool /* include_tls_channel_id */,
                      int /* request_id */)
 
+// Same as ExtensionHostMsg_OpenChannelToExtension, but assigns the port id
+// synchronously.
+IPC_SYNC_MESSAGE_CONTROL4_1(ExtensionHostMsg_OpenChannelToExtensionSync,
+                            int /* frame_routing_id */,
+                            ExtensionMsg_ExternalConnectionInfo,
+                            std::string /* channel_name */,
+                            bool /* include_tls_channel_id */,
+                            int /* port_id */)
+
 // The response to a request to open an extension message port, including the
 // global port id and the request id.
 IPC_MESSAGE_ROUTED2(ExtensionMsg_AssignPortId,
                     int /*port_id */,
                     int /* request_id */)
 
 IPC_MESSAGE_CONTROL3(ExtensionHostMsg_OpenChannelToNativeApp,
                      int /* frame_routing_id */,
                      std::string /* native_app_name */,
                      int /* request_id */)
@@ skipping 196 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 */)