Refactor alternate protocol dictionary parsing.

This CL breaks out into its own function the parsing of a DictionaryValue to
AlternateProtocolInfo.  This is only called once now, but as soon as we start
storing multiple entries per server, we'll need to call it multiple times.  See
https://codereview.chromium.org/665083009/#ps460001.

BUG=392575

Review URL: https://codereview.chromium.org/897313002

Cr-Commit-Position: refs/heads/master@{#314890}
2 files changed