Bug 1540625 - Fix isInWarningGroup invalid PropTypes. r=Honza.

The propType is changed to *not* required as the function is
only passed when the grouping pref is true.

Differential Revision: https://phabricator.services.mozilla.com/D25560

--HG--
extra : moz-landing-system : lando

devtools/client/webconsole/components/ConsoleOutput.js

@@ -61,7 +61,7 @@ class ConsoleOutput extends Component {
       messagesTableData: PropTypes.object.isRequired,
       messagesRepeat: PropTypes.object.isRequired,
       warningGroups: PropTypes.object.isRequired,
-      isInWarningGroup: PropTypes.isRequired,
+      isInWarningGroup: PropTypes.func,
       networkMessagesUpdate: PropTypes.object.isRequired,
       visibleMessages: PropTypes.array.isRequired,
       networkMessageActiveTabId: PropTypes.string.isRequired,