Socket Pool: Inline ClientSocketPoolBaseHelper, 3 of 4

This CL removes ClientSocketPoolBase and makes TransportClientSocketPool
inherit from ClientSocketPoolBaseHelper (Which is where all the logic
lives) instead.  ClientSocketPoolBaseHelper now also inherits from
ClientSocketPool.  A followup CL will merge the two classes.

Change-Id: Ibf6565777df6268928a90a0177736ca082afdf29
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1532665
Commit-Queue: Matt Menke <[email protected]>
Reviewed-by: Asanka Herath <[email protected]>
Cr-Commit-Position: refs/heads/master@{#644017}
7 files changed