code: public void trackPendingDialogCall(FacebookDialog.PendingCall pendingCall) {
          if (pendingFacebookDialogCall != null) {
              // If one is already pending, cancel it; we don't allow multiple pending calls.
              Log.i("Facebook", "Tracking new app call while one is still pending; canceling pending call.");
              cancelPendingAppCall(null);
          }
          pendingFacebookDialogCall = pendingCall;
      }
docs: Register that we are expecting results from a call to the Facebook application (e.g., from a native
  dialog provided by the Facebook app). Activity results forwarded to onActivityResults will be parsed
  and handled if they correspond to this call. Only a single pending FacebookDialog call can be tracked
  at a time; attempting to track another one will cancel the first one.
  @param appCall an PendingCall object containing the call ID