[dart:html] Update WebCore and remove idl_parser dependency
[dart:html] Update WebCore and remove idl_parser dependency

Removes idl_parser dependency as it's now in WebCore and updates
the revision to point to the latest WebCore revision, which includes
the Python 3 migration and idl_parser migration.

Change-Id: Ie24bad3258c44fcfe8ef98ca4dae8846a323a1b6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/212629
Reviewed-by: Riley Porter <1b4d70a146dadc0b64cc886a93a8a324abb72aeb@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk