Support variable substitution and tryserver- and waterfall-only cmd line args.

scripts/slave/recipes/chromium.expected/dynamic_gtest.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "chromium.linux",
       "--builder",
       "Linux Tests",
@@ skipping 122 matching lines @@
       "@@@STEP_LOG_LINE@json.output@    \"gtest_tests\": [@@@",
       "@@@STEP_LOG_LINE@json.output@      \"base_unittests\", @@@",
       "@@@STEP_LOG_LINE@json.output@      {@@@",
       "@@@STEP_LOG_LINE@json.output@        \"shard_index\": 0, @@@",
       "@@@STEP_LOG_LINE@json.output@        \"test\": \"browser_tests\", @@@",
       "@@@STEP_LOG_LINE@json.output@        \"total_shards\": 2@@@",
       "@@@STEP_LOG_LINE@json.output@      }, @@@",
       "@@@STEP_LOG_LINE@json.output@      {@@@",
       "@@@STEP_LOG_LINE@json.output@        \"name\": \"renamed_content_unittests\", @@@",
       "@@@STEP_LOG_LINE@json.output@        \"test\": \"content_unittests\"@@@",
+      "@@@STEP_LOG_LINE@json.output@      }, @@@",
+      "@@@STEP_LOG_LINE@json.output@      {@@@",
+      "@@@STEP_LOG_LINE@json.output@        \"args\": [@@@",
+      "@@@STEP_LOG_LINE@json.output@          \"--correct-common-arg\"@@@",
+      "@@@STEP_LOG_LINE@json.output@        ], @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"non_precommit_args\": [@@@",
+      "@@@STEP_LOG_LINE@json.output@          \"--these-args-should-be-present\", @@@",
+      "@@@STEP_LOG_LINE@json.output@          \"--test-machine-name=\\\"${buildername}\\\"\", @@@",
+      "@@@STEP_LOG_LINE@json.output@          \"--build-revision=\\\"${got_revision}\\\"\"@@@",
+      "@@@STEP_LOG_LINE@json.output@        ], @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"precommit_args\": [@@@",
+      "@@@STEP_LOG_LINE@json.output@          \"--SHOULD-NOT-BE-PRESENT-DURING-THE-RUN\"@@@",
+      "@@@STEP_LOG_LINE@json.output@        ], @@@",
+      "@@@STEP_LOG_LINE@json.output@        \"test\": \"gl_unittests\"@@@",
       "@@@STEP_LOG_LINE@json.output@      }@@@",
       "@@@STEP_LOG_LINE@json.output@    ]@@@",
       "@@@STEP_LOG_LINE@json.output@  }@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
   },
   {
     "cmd": [
       "python",
@@ skipping 156 matching lines @@
       "gtest-results/content_unittests",
       "--builder-name=Linux Tests",
       "--slave-name=TestSlavename",
       "--build-number=571",
       "content_unittests"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "renamed_content_unittests"
   },
   {
+    "allow_subannotations": true,
+    "cmd": [
+      "python",
+      "-u",
+      "[SLAVE_BUILD]/src/infra/scripts/runtest_wrapper.py",
+      "--path-build",
+      "[BUILD]",
+      "--",
+      "--target",
+      "Release",
+      "--xvfb",
+      "--factory-properties",
+      "{\"blamelist\": [\"cool_dev1337@chromium.org\", \"hax@chromium.org\"], \"buildername\": \"Linux Tests\", \"buildnumber\": 571, \"mastername\": \"chromium.linux\", \"parent_buildername\": \"Linux Builder\", \"recipe\": \"chromium\", \"slavename\": \"TestSlavename\", \"workdir\": \"/path/to/workdir/TestSlavename\"}",
+      "--build-properties",
+      "{\"blamelist\": [\"cool_dev1337@chromium.org\", \"hax@chromium.org\"], \"buildername\": \"Linux Tests\", \"buildnumber\": 571, \"mastername\": \"chromium.linux\", \"parent_buildername\": \"Linux Builder\", \"recipe\": \"chromium\", \"slavename\": \"TestSlavename\", \"workdir\": \"/path/to/workdir/TestSlavename\"}",
+      "--annotate=gtest",
+      "--test-type=gl_unittests",
+      "--step-name=gl_unittests",
+      "--test-launcher-summary-output",
+      "/path/to/tmp/json",
+      "--generate-json-file",
+      "-o",
+      "gtest-results/gl_unittests",
+      "--builder-name=Linux Tests",
+      "--slave-name=TestSlavename",
+      "--build-number=571",
+      "gl_unittests",
+      "--correct-common-arg",
+      "--these-args-should-be-present",
+      "--test-machine-name=\"Linux Tests\"",
+      "--build-revision=\"f27fede2220bcd326aee3e86ddfd4ebd0fe58cb9\""
+    ],
+    "cwd": "[SLAVE_BUILD]",
+    "name": "gl_unittests"
+  },
+  {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]