Refactor the way that TestApi works so that it is actually useful.

scripts/slave/recipes/run_presubmit.py

Index: scripts/slave/recipes/run_presubmit.py
diff --git a/scripts/slave/recipes/run_presubmit.py b/scripts/slave/recipes/run_presubmit.py
index e90db09169111de69c55268f40f22eb896d626a9..c3843f8187922dcb75c674f0d855a4edc2261dd4 100644
--- a/scripts/slave/recipes/run_presubmit.py
+++ b/scripts/slave/recipes/run_presubmit.py
@@ -50,14 +50,11 @@ def GenSteps(api):
 
 def GenTests(api):
   for repo_name in ['blink', 'blink_bare', 'tools_build', 'chromium']:
+    extra = {}
     if 'blink' in repo_name:
-      props = api.properties_tryserver(
-        root='src/third_party/WebKit'
-      )
-    else:
-      props = api.properties_tryserver()
-
-    props['repo_name'] = repo_name
-    yield repo_name, {
-      'properties': props
-    }
+      extra['root'] = 'src/third_party/WebKit'
+
+    yield api.Test(repo_name) + api.properties.tryserver(
+      repo_name=repo_name,
+      **extra
+    )