Move the serial API to extensions/.

extensions/common/api/BUILD.gn

 # 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.
 
 import("//extensions/generated_extensions_api.gni")
 
 generated_extensions_api("extensions_api") {
   sources = [
     "app_runtime.idl",
     "dns.idl",
     "extensions_manifest_types.json",
     "power.idl",
+    "serial.idl",
     "socket.idl",
     "sockets_tcp.idl",
     "sockets_tcp_server.idl",
     "sockets_udp.idl",
     "storage.json",
     "test.json",
   ]
   root_namespace = "extensions::core_api"
   impl_dir = "//extensions/browser/api"
   bundle = true
-  deps = [ "//skia" ]
+  deps = [
+    "//device/serial",
+    "//skia",
+  ]
 }