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The API will be defined in a follow-up Blink CL. Unlike the existing,
Service Worker-specific API, this one passes ownership of the new
object to the caller. The origin is specified by a database identifier
derived from the SecurityOrigin on the Blink side.

BUG=439389

Review URL: https://codereview.chromium.org/1031063002

Cr-Commit-Position: refs/heads/master@{#322278}