Add metadata to messages emitted by live tests.

json_reporter.schema.json

 {
   "$schema": "http://json-schema.org/draft-04/schema#",
   "description": "An event emitted by the test package's JSON reporter",
 
   "definitions": {
     "GroupEntry": {
       "required": [
         "id",
         "suiteID",
         "metadata",
@@ skipping 124 matching lines @@
     {
       "title": "GroupEvent",
       "required": ["group"],
       "properties": {
         "type": {"enum": ["group"]},
         "group": {"$ref": "#/definitions/Group"}
       }
     },
 
     {
-      "title": "PrintEvent",
-      "required": ["testID", "message"],
+      "title": "MessageEvent",
+      "required": ["testID", "message", "type"],
       "properties": {
         "type": {"enum": ["print"]},
         "testID": {"type": "integer", "minimum": 0},
-        "message": {"type": "string"}
+        "message": {"type": "string"},
+        "messageType": {"type": "string", "enum": ["print", "skip"]}
       }
     },
 
     {
       "title": "ErrorEvent",
       "required": ["testID", "error", "stackTrace", "isFailure"],
       "properties": {
         "type": {"enum": ["error"]},
         "testID": {"type": "integer", "minimum": 0},
         "error": {"type": "string"},
@@ skipping 33 matching lines @@
             "enum": [
               "start", "testStart", "allSuites", "suite", "group", "print",
               "error", "testDone", "done"
             ]
           }
         }
       }
     }
   ]
 }