WebRTC: Add rtc_stats_unittests to the test suite

scripts/slave/recipes/webrtc/standalone.expected/tryserver_webrtc_linux_memcheck.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]/linux_memcheck",
       "511"
     ],
     "name": "makedirs checkout path",
@@ skipping 492 matching lines @@
       "-u",
       "RECIPE_PACKAGE_REPO[build]/scripts/slave/runtest.py",
       "--target",
       "Release",
       "--xvfb",
       "--factory-properties",
       "{\"BUILD_CONFIG\": \"Release\", \"buildername\": \"linux_memcheck\", \"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\": \"linux_memcheck\", \"buildnumber\": 1337, \"issue\": 666666, \"mastername\": \"tryserver.webrtc\", \"patchset\": 1, \"path_config\": \"kitchen\", \"recipe\": \"webrtc/standalone\", \"revision\": \"12345\", \"rietveld\": \"https://fake.rietveld.url\", \"slavename\": \"slavename\"}",
       "--annotate=gtest",
+      "--test-type=rtc_stats_unittests",
+      "--step-name=rtc_stats_unittests",
+      "--builder-name=linux_memcheck",
+      "--slave-name=slavename",
+      "--build-number=1337",
+      "--revision=f27fede2220bcd326aee3e86ddfd4ebd0fe58cb9",
+      "--pass-build-dir",
+      "--pass-target",
+      "--run-shell-script",
+      "[BUILDER_CACHE]/linux_memcheck/src/tools/valgrind-webrtc/webrtc_tests.sh",
+      "--test",
+      "rtc_stats_unittests",
+      "--tool",
+      "memcheck"
+    ],
+    "cwd": "[BUILDER_CACHE]/linux_memcheck",
+    "name": "rtc_stats_unittests"
+  },
+  {
+    "allow_subannotations": true,
+    "cmd": [
+      "python",
+      "-u",
+      "RECIPE_PACKAGE_REPO[build]/scripts/slave/runtest.py",
+      "--target",
+      "Release",
+      "--xvfb",
+      "--factory-properties",
+      "{\"BUILD_CONFIG\": \"Release\", \"buildername\": \"linux_memcheck\", \"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\": \"linux_memcheck\", \"buildnumber\": 1337, \"issue\": 666666, \"mastername\": \"tryserver.webrtc\", \"patchset\": 1, \"path_config\": \"kitchen\", \"recipe\": \"webrtc/standalone\", \"revision\": \"12345\", \"rietveld\": \"https://fake.rietveld.url\", \"slavename\": \"slavename\"}",
+      "--annotate=gtest",
       "--test-type=rtc_unittests",
       "--step-name=rtc_unittests",
       "--builder-name=linux_memcheck",
       "--slave-name=slavename",
       "--build-number=1337",
       "--revision=f27fede2220bcd326aee3e86ddfd4ebd0fe58cb9",
       "--pass-build-dir",
       "--pass-target",
       "--run-shell-script",
       "[BUILDER_CACHE]/linux_memcheck/src/tools/valgrind-webrtc/webrtc_tests.sh",
@@ skipping 228 matching lines @@
     ],
     "cwd": "[BUILDER_CACHE]/linux_memcheck",
     "name": "webrtc_nonparallel_tests"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]