Fix crash when closing tabs

- There was an issue when scheduleRemoveTab is called
  before tryRemoveTab call is completed. This caused
  callbacks set by the older tab to fire even after the
  tab was removed.The current fix is to
  remove older callbacks once the tab is removed.

Change-Id: I65adb6131df26deb2312357103d665f3970b7a0e
1 file changed