Verify alternative server certificate validity for origin.
Verify that the certificate presented by the alternative server is valid for the
origin when using HTTP/2, both when opening a new connection or when pooling to
an existing one.
Patch Set 1:
* Enable hopping to a different host for HTTP/2 (not for QUIC).
* Add unittests for both new connection and pooling cases. Note in trybot
output that *Valid tests pass and *Invalid tests fail.
Patch Set 2 and up:
* Verify certificate validity in HttpStreamFactoryImpl::Job.
BUG=474217
Review URL: https://codereview.chromium.org/
1074193003
Cr-Commit-Position: refs/heads/master@{#327293}