protected @Nullable String getCallerContextString() {
    Object cc = getCallerContext();
    if (cc == null) {
      return null;
    }
    return cc.toString();
  }
updateDebugOverlay updates the debug overlay. Subclasses of {@link PipelineDraweeController}
can override this method (and call <code>super</code>) to provide additional debug information.
drawee-backends/drawee-pipeline/src/main/java/com/facebook/drawee/backends/pipeline/PipelineDraweeController.java