Add an Android sample app for Telemetry tests.

tools/perf/perf_helper_app/BUILD.gn

+# Copyright 2016 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("//build/config/android/rules.gni")
+import("//testing/test.gni")
+
+# Mark all targets as test only.
+testonly = true
+
+android_apk("perf_helper_apk") {
+  apk_name = "PerfHelper"
+  java_files =
+      [ "src/org/chromium/perf_helper/PushAppsToBackgroundActivity.java" ]
+  android_manifest = "AndroidManifest.xml"
+  deps = [
+    ":perf_helper_apk_resources",
+  ]
+}
+
+android_resources("perf_helper_apk_resources") {
+  resource_dirs = [ "res" ]
+  custom_package = "org.chromium.perf_helper"
+}