Devtools: allow multiple custom formatters

Source/devtools/protocol.json

 {
     "version": { "major": "1", "minor": "1" },
     "domains": [{
         "domain": "Inspector",
         "hidden": true,
         "types": [],
         "commands": [
             {
                 "name": "enable",
                 "description": "Enables inspector domain notifications."
@@ skipping 734 matching lines @@
                     { "name": "objectId", "$ref": "RemoteObjectId", "optional": true, "description": "Unique object identifier (for non-primitive values)." },
                     { "name": "preview", "$ref": "ObjectPreview", "optional": true, "description": "Preview containing abbreviated property values. Specified for <code>object</code> type values only.", "hidden": true },
                     { "name": "customPreview", "$ref": "CustomPreview", "optional": true, "hidden": true}
                 ]
             },
             {   "id": "CustomPreview",
                 "type": "object",
                 "hidden": true,
                 "properties": [
                     { "name": "header", "type": "string"},
-                    { "name": "hasBody", "type": "boolean"}
+                    { "name": "hasBody", "type": "boolean"},
+                    {"name": "formatterObjectId", "$ref": "RemoteObjectId"}
                 ]
             },
             {
                 "id": "ObjectPreview",
                 "type": "object",
                 "hidden": true,
                 "description": "Object containing abbreviated remote object value.",
                 "properties": [
                     { "name": "type", "type": "string", "enum": ["object", "function", "undefined", "string", "number", "boolean", "symbol"], "description": "Object type." },
                     { "name": "subtype", "type": "string", "optional": true, "enum": ["array", "null", "node", "regexp", "date", "map", "set", "iterator", "generator", "error"], "description": "Object subtype hint. Specified for <code>object</code> type values only." },
@@ skipping 4304 matching lines @@
                 ],
                 "returns": [
                     { "name": "accessibilityNode", "$ref": "AXNode", "description": "The <code>Accessibility.AXNode</code> for this DOM node, if it exists.", "optional": true }
                 ],
                 "description": "Fetches the accessibility node for this DOM node, if it exists.",
                 "hidden": true
             }
         ]
     }]
 }