Bug 1465635 - Ensure removing BrowsingContextTarget front events when destroying it. r=jdescottes

When destroying the target, Target.destroy (for local tabs) only calls DebuggerClient.close,
which isn't going to call `detach`. But we still do need to unregister
the tabNavigated/frameUpdate listener to prevent unecessary event from firing.

Depends on D17609

Differential Revision: https://phabricator.services.mozilla.com/D17610

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

devtools/shared/fronts/targets/browsing-context.js

@@ -169,6 +169,17 @@ class BrowsingContextTargetFront extends
 
     return response;
   }
+
+  destroy() {
+    const promise = super.destroy();
+
+    // As detach isn't necessarily called on target's destroy
+    // (it isn't for local tabs), ensure removing listeners set in attach.
+    this.off("tabNavigated", this._onTabNavigated);
+    this.off("frameUpdate", this._onFrameUpdate);
+
+    return promise;
+  }
 }
 
 exports.BrowsingContextTargetFront = BrowsingContextTargetFront;