SocketPools: group_name to GroupId conversion part 4 (last part).

Make ClientSocketPool methods take GroupIds instead of string group
names, and remove implicit conversion from GroupId to std::string.

This is part of an effort to merge ClientSocketPool::SocketParams and
group names / GroupIds.

Bug: 533571
Change-Id: I8a4548b1ed55070fe55449e8eac36be9768481f6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1525991
Commit-Queue: Matt Menke <mmenke@chromium.org>
Reviewed-by: David Benjamin <davidben@chromium.org>
Cr-Commit-Position: refs/heads/master@{#642042}
17 files changed