Port custom_tabs_client from GYP to GN

BUILD.gn

 # Copyright (c) 2013 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.
 
 # This is the root build file for GN. GN will start processing by loading this
 # file, and recursively load all dependencies until all dependencies are either
 # resolved or known not to exist (which will cause the build to fail). So if
 # you add a new build file, there must be some path of dependencies from this
 # file to your new one or GN won't know about it.
 
@@ skipping 299 matching lines @@
       "//tools/gn:gn_unittests",
       "//ui/app_list:app_list_unittests",
       "//url:url_unittests",
     ]
 
     if (!is_chromecast) {
       deps += [
         "//chrome/android:chrome_public_apk",
         "//chrome/android:chrome_public_test_apk",
         "//chrome/test/chromedriver/test/webview_shell:chromedriver_webview_shell_apk",
+        "//third_party/custom_tabs_client:custom_tabs_client_example_apk",
       ]
     }
 
     if (has_chrome_android_internal) {
       deps += [ "//clank" ]  # TODO(GYP) ??
     }
   }
 
   if (is_linux) {  # TODO(GYP): || is_android || is_bsd?
     deps += [
@@ skipping 679 matching lines @@
       if (target_cpu == "x86") {
         deps += [
           # "//content/shell:crash_service_win64", TODO(GYP): crbug.com/537009
         ]
       }
     } else {
       deps += [ "//breakpad:minidump_stackwalk($host_toolchain)" ]
     }
   }
 }