message: Support undo for background map and AO.
diff: @@ -175,7 +175,9 @@ export class ViewAttributes {
  };
  const enableAO = (enabled: boolean) => {
  - this._vp.view.viewFlags.ambientOcclusion = enabled;
  + const vf = this._vp.view.viewFlags.clone(this._scratchViewFlags);
  + vf.ambientOcclusion = enabled;
  + this._vp.view.viewFlags = vf;
  showHideDropDowns(enabled);
  this.sync();
  };
  @@ -333,7 +335,9 @@ export class ViewAttributes {
  };
  const enableMap = (enabled: boolean) => {
  - this._vp.view.viewFlags.backgroundMap = enabled;
  + const vf = this._vp.view.viewFlags.clone(this._scratchViewFlags);
  + vf.backgroundMap = enabled;
  + this._vp.view.viewFlags = vf;
  showHideDropDowns(enabled);
  this.sync();
  };
  