WebRTC: Add rtc_stats_unittests to the test suite

scripts/slave/recipes/webrtc/standalone.expected/tryserver_webrtc_android_n6.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]/android_n6",
       "511"
     ],
     "name": "makedirs checkout path",
@@ skipping 570 matching lines @@
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json",
       "PATH": "[BUILDER_CACHE]/android_n6/src/third_party/android_tools/sdk/platform-tools:[BUILDER_CACHE]/android_n6/src/build/android:%(PATH)s"
     },
     "name": "peerconnection_unittests"
   },
   {
     "cmd": [
       "python",
       "-u",
+      "[BUILDER_CACHE]/android_n6/src/out/Debug/bin/run_rtc_stats_unittests",
+      "--blacklist-file",
+      "[BUILDER_CACHE]/android_n6/src/out/bad_devices.json",
+      "--verbose",
+      "--adb-path",
+      "[BUILDER_CACHE]/android_n6/src/third_party/android_tools/sdk/platform-tools/adb"
+    ],
+    "cwd": "[BUILDER_CACHE]/android_n6",
+    "env": {
+      "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json",
+      "PATH": "[BUILDER_CACHE]/android_n6/src/third_party/android_tools/sdk/platform-tools:[BUILDER_CACHE]/android_n6/src/build/android:%(PATH)s"
+    },
+    "name": "rtc_stats_unittests"
+  },
+  {
+    "cmd": [
+      "python",
+      "-u",
       "[BUILDER_CACHE]/android_n6/src/out/Debug/bin/run_rtc_unittests",
       "--blacklist-file",
       "[BUILDER_CACHE]/android_n6/src/out/bad_devices.json",
       "--verbose",
       "--adb-path",
       "[BUILDER_CACHE]/android_n6/src/third_party/android_tools/sdk/platform-tools/adb"
     ],
     "cwd": "[BUILDER_CACHE]/android_n6",
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json",
@@ skipping 238 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@  os.remove(report)@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]