http://src.chromium.org/viewvc/chrome/trunk/src/chrome/common/extensions/api/extension_api.json[ { "namespace": "extension", "types": [ { "id": "MessageSender", "type": "object", "description": "An object containing information about the script context that sent a message or request.", "properties": { "tab": {"$ref": "Tab", "optional": true, "description":"This property will only be present when the connection was opened from a tab or content script."}, "id": {"type": "string", "description
