Rename, refactor, and document "HttpServerProperties::SupportsQuic()"

This method name is confusing, since
HttpServerProperties::SupportsSpdy() is used to store whether a server
supports SPDY/H2, but SupportsQuic() actually means a network where
QUIC works (i.e., the ISP isn't breaking QUIC, or something similar).
This difference in meaning was also not documented anywhere.

This CL renames "SupportsQuic" to "LastLocalAddressWhenQuicWorked",
adds documentation, and reworks the API slightly - its behavior
around empty IPAddresses was a little weird, as was passing in an
IPAddress() and a bool when clearing information for all IP addresses.

This CL also renames QuicFactory::requires_confirmation_ to
is_quic_known_to_work_on_current_network_ (which also requires
inverting its value) and adds some documentation for it, as it was
similarly confusing.

Bug: 969890
Change-Id: Id51b082343ff31ecd36f1bedfab8342307da26ee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1790325
Commit-Queue: Matt Menke <[email protected]>
Reviewed-by: Ryan Hamilton <[email protected]>
Reviewed-by: Zhongyi Shi <[email protected]>
Cr-Commit-Position: refs/heads/master@{#695833}
14 files changed