Update navigation API deferred commit prototype to use new precommitHandler mechanism

Explainer updates:
WICG/navigation-api#281
WICG/navigation-api#282

Change-Id: I210f47c1dba5064e069e5df059d706cb9d8ecb21
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6382278
Commit-Queue: Nate Chapin <[email protected]>
Reviewed-by: Domenic Denicola <[email protected]>
Reviewed-by: Noam Rosenthal <[email protected]>
Reviewed-by: Alex Moshchuk <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1438913}

Author: natechapin