WebRTC: Add rtc_stats_unittests to the test suite

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

 [
   {
     "cmd": [
       "RECIPE_PACKAGE_REPO[build]/scripts/slave/ios/host_info.py",
       "--json-file",
       "/path/to/tmp/json"
     ],
     "name": "host and tools info",
     "~followup_annotations": [
       "@@@STEP_TEXT@<br />OS X 1.2.3, Xcode 6.7.8 (5D342509a)@@@",
@@ skipping 477 matching lines @@
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]/scripts/slave/runtest.py",
       "--target",
       "Release",
       "--factory-properties",
       "{\"BUILD_CONFIG\": \"Release\", \"buildername\": \"mac_rel\", \"buildnumber\": 1337, \"issue\": 666666, \"mastername\": \"tryserver.webrtc\", \"patchset\": 1, \"path_config\": \"kitchen\", \"recipe\": \"webrtc/standalone\", \"revision\": \"12345\", \"rietveld\": \"https://fake.rietveld.url\", \"slavename\": \"slavename\"}",
       "--build-properties",
       "{\"BUILD_CONFIG\": \"Release\", \"buildername\": \"mac_rel\", \"buildnumber\": 1337, \"issue\": 666666, \"mastername\": \"tryserver.webrtc\", \"patchset\": 1, \"path_config\": \"kitchen\", \"recipe\": \"webrtc/standalone\", \"revision\": \"12345\", \"rietveld\": \"https://fake.rietveld.url\", \"slavename\": \"slavename\"}",
+      "--test-type=rtc_stats_unittests",
+      "--step-name=rtc_stats_unittests",
+      "--builder-name=mac_rel",
+      "--slave-name=slavename",
+      "--build-number=1337",
+      "--run-python-script",
+      "--revision=f27fede2220bcd326aee3e86ddfd4ebd0fe58cb9",
+      "[BUILDER_CACHE]/mac_rel/src/third_party/gtest-parallel/gtest-parallel",
+      "[BUILDER_CACHE]/mac_rel/src/out/Release/rtc_stats_unittests",
+      "--"
+    ],
+    "cwd": "[BUILDER_CACHE]/mac_rel",
+    "name": "rtc_stats_unittests"
+  },
+  {
+    "cmd": [
+      "python",
+      "-u",
+      "RECIPE_PACKAGE_REPO[build]/scripts/slave/runtest.py",
+      "--target",
+      "Release",
+      "--factory-properties",
+      "{\"BUILD_CONFIG\": \"Release\", \"buildername\": \"mac_rel\", \"buildnumber\": 1337, \"issue\": 666666, \"mastername\": \"tryserver.webrtc\", \"patchset\": 1, \"path_config\": \"kitchen\", \"recipe\": \"webrtc/standalone\", \"revision\": \"12345\", \"rietveld\": \"https://fake.rietveld.url\", \"slavename\": \"slavename\"}",
+      "--build-properties",
+      "{\"BUILD_CONFIG\": \"Release\", \"buildername\": \"mac_rel\", \"buildnumber\": 1337, \"issue\": 666666, \"mastername\": \"tryserver.webrtc\", \"patchset\": 1, \"path_config\": \"kitchen\", \"recipe\": \"webrtc/standalone\", \"revision\": \"12345\", \"rietveld\": \"https://fake.rietveld.url\", \"slavename\": \"slavename\"}",
       "--test-type=rtc_unittests",
       "--step-name=rtc_unittests",
       "--builder-name=mac_rel",
       "--slave-name=slavename",
       "--build-number=1337",
       "--run-python-script",
       "--revision=f27fede2220bcd326aee3e86ddfd4ebd0fe58cb9",
       "[BUILDER_CACHE]/mac_rel/src/third_party/gtest-parallel/gtest-parallel",
       "[BUILDER_CACHE]/mac_rel/src/out/Release/rtc_unittests",
       "--"
@@ skipping 174 matching lines @@
     ],
     "cwd": "[BUILDER_CACHE]/mac_rel",
     "name": "webrtc_nonparallel_tests"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]