Support data URL for cert-url of Signed HTTP Exchange.

Data URL for cert-url had been supported.
But after crrev.com/c/1577483 which landed in 76.0.3774.0, Chrome failes
to load the data URL when NetworkService is enabled.

To fix this issue, this CL change SignedExchangeCertFetcher to use
DataURLLoaderFactory when the cert-url's scheme is "data:".

Bug: 966736,939871
Change-Id: I352caf29e54f288371f18266597f5374ab7ca2bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1628488
Reviewed-by: Kunihiko Sakamoto <ksakamoto@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Tsuyoshi Horo <horo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662980}
5 files changed