Method _watchDrawerPosition

src/material/sidenav/drawer.ts:981–987

* Subscribes to drawer onPositionChanged event in order to * re-validate drawers when the position changes.

(drawer: MatDrawer)

   * re-validate drawers when the position changes.
   */
  private _watchDrawerPosition(drawer: MatDrawer): void {
    // NOTE: We need to wait for the microtask queue to be empty before validating,
    // since both drawers may be swapping positions at the same time.
    drawer.onPositionChanged.pipe(takeUntil(this._drawers.changes)).subscribe(() => {
      afterNextRender({read: () => this._validateDrawers()}, {injector: this._injector});
    });
  }

  /** Subscribes to changes in drawer mode so we can run change detection. */
  private _watchDrawerMode(drawer: MatDrawer): void {