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

recipe_modules/raw_io/example.expected/basic.json

 [
   {
     "cmd": [
       "echo",
       "Hello World"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "echo",
     "stderr": "/path/to/tmp/",
     "stdout": "/path/to/tmp/"
@@ skipping 46 matching lines @@
   },
   {
     "cmd": [
       "ls",
       "[SLAVE_BUILD]/out"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "leak dir"
   },
   {
+    "cmd": [
+      "python",
+      "-u",
+      "\nimport sys\nwith open(sys.argv[1], 'w') as f:\n  f.write('bad_value')\n",
+      "/path/to/tmp/"
+    ],
+    "cwd": "[SLAVE_BUILD]",
+    "name": "override_default_mock",
+    "~followup_annotations": [
+      "@@@STEP_LOG_LINE@python.inline@@@@",
+      "@@@STEP_LOG_LINE@python.inline@import sys@@@",
+      "@@@STEP_LOG_LINE@python.inline@with open(sys.argv[1], 'w') as f:@@@",
+      "@@@STEP_LOG_LINE@python.inline@  f.write('bad_value')@@@",
+      "@@@STEP_LOG_END@python.inline@@@"
+    ]
+  },
+  {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]