Add an Android sample app for Telemetry tests.

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 266 matching lines @@
       "//content/public/android:content_junit_tests",
       "//content/shell/android:content_shell_apk",
       "//content/test:video_decode_accelerator_unittest",
       "//net/android:net_junit_tests",
       "//testing/android/junit:junit_unittests",
       "//third_party/android_tools:uiautomator_java",
       "//third_party/errorprone:chromium_errorprone",
       "//third_party/smhasher:murmurhash3",
       "//tools/android:android_tools",
       "//tools/android:memconsumer",
+      "//tools/android:push_apps_to_background",
       "//tools/android/heap_profiler:heap_profiler_unittests",
       "//tools/android/kerberos/SpnegoAuthenticator:spnego_authenticator_apk",
       "//tools/cygprofile:cygprofile_unittests",
       "//tools/imagediff($host_toolchain)",
       "//ui/android:ui_junit_tests",
     ]
     deps -= [
       "//net:net_perftests",
       "//url:url_unittests",
     ]
@@ skipping 602 matching lines @@
   assert(target_name != "")  # Mark as used.
   sources = invoker.actual_sources
   assert(
       sources == invoker.actual_sources,
       "Do not use a platform name in your output directory (found \"$root_build_dir\"). http://crbug.com/548283")
 }
 
 assert_valid_out_dir("_unused") {
   actual_sources = [ "$root_build_dir/foo" ]
 }