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We are trying to show SignedExchange related information in DevTools.
https://bit.ly/2HXVbCU

This CL adds LayoutTests and -expected.txt files to track the progress
of the implementation.

Currently there are some difference from the ideal behavior:
- The status code of the succeeded .htxg should be 200. Currenly it is
  302 which is the status code of internally generated redirect
  response.
- The status code of the invalid .htxg should be 200. Currenly it is 0
  because the actual response is not sent to DevTools. DevTools just
  recieves "loadingFailed" event.
- The request to the certificate file shold be displayed. Currenly
  DevTools doesn't recieve the certificate request which is sent from
  the browser process.
- There is no signed exchange related information in the network log.

Bug: 830505
Change-Id: I80c4c648c466505fef4f729eb046a91ede4a4660
Reviewed-on: https://chromium-review.googlesource.com/1027574
Commit-Queue: Tsuyoshi Horo <horo@chromium.org>
Reviewed-by: Kunihiko Sakamoto <ksakamoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553882}