erverFlush_() {
    const records = this.observer_.takeRecords();
    if (records.length) {
      this.didTargetMutate_(records);
    }
  },

  didTargetMutate_(e) {
    const modeSize = this.targetSizesByModeKey_[this.modeKey_];
    if (modeSize !== undefined) {
      this.setTargetSize_(modeSize);
      return;
    }

    // If we hadn't previously sized the target, then just remove any manual
    // sizing that we applied.
    this.target_.style[this.targetStyleKey_] = '';
  },

  get targetStyleKey_() {