use _getFocusedElementPierceShadowDom

Author: Caleb Kish

src/material/timepicker/timepicker-input.ts

@@ -42,7 +42,7 @@ import {Subscription} from 'rxjs';
 import {DOWN_ARROW, ESCAPE, hasModifierKey, UP_ARROW} from '@angular/cdk/keycodes';
 import {validateAdapter} from './util';
 import {DOCUMENT} from '@angular/common';
-import {_getShadowRoot} from '../../cdk/platform';
+import {_getFocusedElementPierceShadowDom} from '../../cdk/platform';
 
 /**
  * Input that can be used to enter time and connect to a `mat-timepicker`.
@@ -407,8 +407,7 @@ export class MatTimepickerInput<D> implements ControlValueAccessor, Validator, O
 
   /** Whether the input is currently focused. */
   private _hasFocus(): boolean {
-    const root = _getShadowRoot(this._elementRef.nativeElement) || this._document;
-    return root.activeElement === this._elementRef.nativeElement;
+    return _getFocusedElementPierceShadowDom() === this._elementRef.nativeElement;
   }
 
   /** Gets a function that can be used to validate the input. */