Bug 1455737 - Remove the result object from DownloadHistory when removing the view r=Mardak

MozReview-Commit-ID: 5Qb5j30eqFO

--HG--
extra : rebase_source : 5a01b533acd7ceee70c23f063bdc889daf7f8311

toolkit/components/downloads/DownloadHistory.jsm

@@ -454,6 +454,17 @@ this.DownloadHistoryList.prototype = {
   },
   _result: null,
 
+  /**
+   * Remove the view that belongs to this list via DownloadList's removeView. In
+   * addition, delete the result object to ensure there are no memory leaks.
+   */
+  removeView(aView) {
+    DownloadList.prototype.removeView.call(this, aView);
+
+    // Clean up any active results that might still be observing. See bug 1455737
+    this.result = null;
+  },
+
   /**
    * Index of the first slot that contains a session download. This is equal to
    * the length of the list when there are no session downloads.