[Extensions] Make port creation synchronous in unload handlers

extensions/common/extension_messages.h

Index: extensions/common/extension_messages.h
diff --git a/extensions/common/extension_messages.h b/extensions/common/extension_messages.h
index f9e9bcb31674e66f6c73de539f2194795d7689aa..115071db982ef1009ecb2a07eb02e1d967bfb842 100644
--- a/extensions/common/extension_messages.h
+++ b/extensions/common/extension_messages.h
@@ -688,6 +688,15 @@ IPC_MESSAGE_CONTROL5(ExtensionHostMsg_OpenChannelToExtension,
                      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,