Add an Android sample app for Telemetry tests.

tools/android/BUILD.gn

Index: tools/android/BUILD.gn
diff --git a/tools/android/BUILD.gn b/tools/android/BUILD.gn
index bcadd0f7f66bd2e8aefc3f098822dc841e8d3c9b..99f9a011a5514e2f086471687bc979c748f799b2 100644
--- a/tools/android/BUILD.gn
+++ b/tools/android/BUILD.gn
@@ -79,3 +79,11 @@ group("audio_focus_grabber") {
     "//tools/android/audio_focus_grabber:audio_focus_grabber_apk",
   ]
 }
+
+# GYP: //tools/android/android_tools.gyp:push_apps_to_background
+group("push_apps_to_background") {
+  testonly = true
+  deps = [
+    "//tools/android/push_apps_to_background:push_apps_to_background_apk",
+  ]
+}