[Android] Fix port leak in the forwarder.

tools/android/BUILD.gn

 # Copyright 2015 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.
 
 # Intermediate target grouping the android tools needed to run native
 # unittests and instrumentation test apks.
 group("android_tools") {
+  testonly = true
   deps = [
     "//build/android:wrapper_scripts",
     "//build/android/pylib/device/commands",
     "//third_party/android_platform:stack_wrapper",
     "//third_party/catapult/telemetry:bitmaptools($host_toolchain)",
     "//tools/android/adb_reboot",
     "//tools/android/file_poller",
     "//tools/android/forwarder2",
     "//tools/android/md5sum",
     "//tools/android/memtrack_helper:memtrack_helper",
@@ skipping 45 matching lines @@
     "//tools/android/audio_focus_grabber:audio_focus_grabber_apk",
   ]
 }
 
 group("push_apps_to_background") {
   testonly = true
   deps = [
     "//tools/android/push_apps_to_background:push_apps_to_background_apk",
   ]
 }