GitLab

This is a reland of 93e10d47. The original
change was reverted due to a clusterfuzz report, but this CL seems innocent so
I'm relanding this.

Original change's description:
> Introduce QuicTransport
>
> This is the first CL to implement QuicTransport. This CL
>  - creates a directory in blink,
>  - introduces a new blink runtime feature flag, and
>  - defines QuicTransport IDL interface behind the flag,
>
> Bug: 1011392
> Change-Id: Id432cee2b6d5df6ab4a4c3e8aa6828d5a7937dd9
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1868569
> Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
> Reviewed-by: Kent Tamura <tkent@chromium.org>
> Reviewed-by: Adam Rice <ricea@chromium.org>
> Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#707303}

TBR=kinuko@chromium.org,ricea@chromium.org,yhirano@chromium.org,tkent@chromium.org

Bug: 1011392, 1016436
Change-Id: Iad9e785cd5886c7b2d2e25fe55f3b5f327727f87
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1880502
Commit-Queue: Kent Tamura <tkent@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709401}