Make output placeholders like json.output index-able by name.

recipe_modules/json/test_api.py

Index: recipe_modules/json/test_api.py
diff --git a/recipe_modules/json/test_api.py b/recipe_modules/json/test_api.py
index 762fada542118a7a19bfee731c3cb57d45ee9d69..186db825e5fd2d691b68be7118b3a4bd3ebfae18 100644
--- a/recipe_modules/json/test_api.py
+++ b/recipe_modules/json/test_api.py
@@ -9,11 +9,12 @@ from recipe_engine import recipe_test_api
 class JsonTestApi(recipe_test_api.RecipeTestApi):
   @recipe_test_api.placeholder_step_data
   @staticmethod
-  def output(data, retcode=None):
-    return json.dumps(data), retcode
+  def output(data, retcode=None, id=None):
+    return json.dumps(data), retcode, id
 
-  def output_stream(self, data, stream='stdout', retcode=None):
+  def output_stream(self, data, stream='stdout', retcode=None, id=None):
     assert stream in ('stdout', 'stderr')
     ret = recipe_test_api.StepTestData()
-    setattr(ret, stream, self.output(data, retcode).unwrap_placeholder())
+    setattr(ret, stream,
+            self.output(data, retcode=retcode, id=id).unwrap_placeholder())
     return ret