Bug 1161072 - Destroy highlighter actor on disconnect. r=pbrosset

toolkit/devtools/server/actors/inspector.js

@@ -3504,7 +3504,9 @@ var InspectorActor = exports.InspectorActor = protocol.ActorClass({
     }
 
     this._highlighterPromise = this.getWalker().then(walker => {
-      return HighlighterActor(this, autohide);
+      let highlighter = HighlighterActor(this, autohide);
+      this.manage(highlighter);
+      return highlighter;
     });
     return this._highlighterPromise;
   }, {