Move RC4 behind a fallback.
This is to start gathering better metrics on which servers require RC4. Many
servers which prefer RC4 will still accept another cipher suite. Moving it
behind a fallback will make our cipher suite metrics reflect roughly servers
which require it and not only those which prefer it.
Note that this sort of fallback provides NO security benefit. If a server
prefers a non-RC4 cipher, they already securely negotiate it whether or not the
client offers RC4. If a server prefers RC4, this kind of fallback does nothing
to prevent an attacker from switching the connection to RC4. This is purely for
measurement.
BUG=375342
Review URL: https://codereview.chromium.org/1052743003
Cr-Commit-Position: refs/heads/master@{#323837}
11 files changed
