code: public AnnotatedLargeText obtainLog() {
          WeakReference<AnnotatedLargeText> l = log;
          if(l==null) return null;
          return l.get();
      }
docs: Obtains the log file.
  
  <p>
  The default implementation get this from {@link #workerThread},
  so when it's complete, the log could be gone any time.
  
  <p>
  Derived classes that persist the text should override this
  method so that it fetches the file from disk.