WebRTC: Add android_junit_tests.

scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_android64_builder.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "\nimport sys, os\npath = sys.argv[1]\nmode = int(sys.argv[2])\nif not os.path.isdir(path):\n  if os.path.exists(path):\n    print \"%s exists but is not a dir\" % path\n    sys.exit(1)\n  os.makedirs(path, mode)\n",
       "[BUILDER_CACHE]/Android64_Builder",
       "511"
     ],
     "name": "makedirs checkout path",
@@ skipping 290 matching lines @@
       "public-read",
       "[SLAVE_BUILD]/AppRTCMobile_apk.zip",
       "gs://chromium-webrtc/client.webrtc/Android64 Builder/AppRTCMobile_apk_170242.zip"
     ],
     "name": "gsutil upload",
     "~followup_annotations": [
       "@@@STEP_LINK@gsutil.upload@https://storage.googleapis.com/chromium-webrtc/client.webrtc/Android64 Builder/AppRTCMobile_apk_170242.zip@@@"
     ]
   },
   {
+    "cmd": [
+      "python",
+      "-u",
+      "[BUILDER_CACHE]/Android64_Builder/src/out/Release/bin/run_android_junit_tests",
+      "--blacklist-file",
+      "[BUILDER_CACHE]/Android64_Builder/src/out/bad_devices.json",
+      "--verbose",
+      "--adb-path",
+      "[BUILDER_CACHE]/Android64_Builder/src/third_party/android_tools/sdk/platform-tools/adb"
+    ],
+    "cwd": "[BUILDER_CACHE]/Android64_Builder",
+    "env": {
+      "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json",
+      "PATH": "[BUILDER_CACHE]/Android64_Builder/src/third_party/android_tools/sdk/platform-tools:[BUILDER_CACHE]/Android64_Builder/src/build/android:%(PATH)s"
+    },
+    "name": "android_junit_tests"
+  },
+  {
     "cmd": [],
     "name": "trigger",
     "trigger_specs": [
       {
         "builder_name": "Android64 Tests (L Nexus9)",
         "properties": {
           "parent_got_revision": "f27fede2220bcd326aee3e86ddfd4ebd0fe58cb9",
           "parent_got_revision_cp": "refs/heads/master@{#170242}",
           "revision": "f27fede2220bcd326aee3e86ddfd4ebd0fe58cb9"
         }
       }
     ],
     "~followup_annotations": [
       "@@@STEP_TEXT@Android64 Tests (L Nexus9)@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]