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

scripts/slave/recipes/chromium_trybot.py

Index: scripts/slave/recipes/chromium_trybot.py
diff --git a/scripts/slave/recipes/chromium_trybot.py b/scripts/slave/recipes/chromium_trybot.py
index 52d6212d91c876ee197385345d2192b03db2e038..5b72741a8956ff8b345b29a648518d21ac8e1059 100644
--- a/scripts/slave/recipes/chromium_trybot.py
+++ b/scripts/slave/recipes/chromium_trybot.py
@@ -217,6 +217,7 @@ def _RunStepsInternal(api):
 
   bot_config_object = api.chromium_tests.create_bot_config_object(
       bot_config['mastername'], bot_config['buildername'])
+  api.chromium_tests.set_precommit_mode()
   api.chromium_tests.configure_build(
       bot_config_object, override_bot_type='builder_tester')
 
@@ -491,6 +492,31 @@ def GenTests(api):
   )
 
   yield (
+    api.test('dynamic_gtest_with_args_on_trybot') +
+    props() +
+    api.platform.name('linux') +
+    api.override_step_data('read test spec', api.json.output({
+        'Linux Tests': {
+            'gtest_tests': [
+                {
+                  'test': 'base_unittests',
+                  'args': ['--correct-common-arg'],
+                  'non_precommit_args': [
+                    '--SHOULD-NOT-BE-PRESENT-DURING-THE-RUN'
+                  ],
+                  'precommit_args': [
+                    '--these-args-should-be-present',
+                    '--test-machine-name=\"${buildername}\"',
+                    '--build-revision=\"${got_revision}\"',
+                  ],
+                },
+            ],
+        },
+    })) +
+    suppress_analyze()
+  )
+
+  yield (
     api.test('swarming_trigger_failure') +
     props() +
     api.platform.name('linux') +