Port custom_tabs_client from GYP to GN

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.
 #
 # GYP: //android/tools/android_tools.gyp:android_tools
 group("android_tools") {
   deps = [
     "//tools/android/forwarder2",
     "//tools/android/md5sum",
   ]
 }
+
+# GYP: //tools/android/android_tools.gyp:customtabs_benchmark
+group("customtabs_benchmark") {
+  deps = [
+    "//tools/android/customtabs_benchmark:customtabs_benchmark_apk",
+  ]
+}