Chrome Version: TOT

Fallback redirection of signed exchange was implemented in  crbug.com/874323 .
But DevTools can't show the fallback redirection correctly yet.

DevTools shows the redirected request in Network panel as if the response is the
content of the signed exchange, even though the response was served from the
server.

Example:

1. Launch Chrome with "--enable-features=SignedHTTPExchange" flag.
2. Open DevTools Network tab.
3. Go "https://htxg-b1.appspot.com/sxg/hello_ec.sxg".
4. Chrome is redirected to "https://sxg-demo.horo.jp/hello_ec.html".
5. The page says "This file is served from the server. Not from SignedExchange."

- "hello_ec.sxg" is signed with an invalid certificate without
  CanSignHttpExchangesDraft extension. So the request of "hello_ec.sxg" should
  be shown as error (with red color).
- "hello_ec.html" is served from the server, not from the signed exchange. So:
  - The Size item of hello_ec.html in NetworkDataGrid should show the actual
    size, not "from signed-exchange".
  - The Status Code item of hello_ec.html in RequestHeadersView should say
    "signed-exchange error fallback" or something, not "from signed-exchange".

Note: When AllowSignedHTTPExchangeCertsWithoutExtension feature is enabled, the
certificate error is ignored, and the content "Hello SignedHTTPExchange" inside
the signed exchange is rendered.