Bug 948805 - Fix TypeError: this._toolbox is null: StyleEditorPanel.prototype._showError; r=pbrosset

browser/devtools/styleeditor/styleeditor-panel.js

@@ -72,15 +72,26 @@ StyleEditorPanel.prototype = {
    *
    * @param  {string} event
    *         Type of event
-   * @param  {string} errorCode
+   * @param  {string} code
    *         Error code of error to report
+   * @param  {string} message
+   *         Extra message to append to error message
    */
-  _showError: function(event, errorCode) {
-    let message = _(errorCode);
+  _showError: function(event, code, message) {
+    if (!this._toolbox) {
+      // could get an async error after we've been destroyed
+      return;
+    }
+
+    let errorMessage = _(code);
+    if (message) {
+      errorMessage += " " + message;
+    }
+
     let notificationBox = this._toolbox.getNotificationBox();
     let notification = notificationBox.getNotificationWithValue("styleeditor-error");
     if (!notification) {
-      notificationBox.appendNotification(message,
+      notificationBox.appendNotification(errorMessage,
         "styleeditor-error", "", notificationBox.PRIORITY_CRITICAL_LOW);
     }
   },