popScope(scope) {
    if (this.scope_ !== scope) {
      throw new Error('BlockBindingTransformer scope mismatch');
    }
    this.scope_ = scope.parent;
    this.blockRenames_ = this.scope_ && this.scope_.blockBindingRenames || [];
  }
Pops scope, tracks proper matching of push_/pop_ operations.
@param {Scope} scope