NetworkContext: Always create the CookieStore and ChannelIDStore

This CL makes NetworkContexts create CookieStores and ChannelIDStores in
the hybrid URLRequestContext creation path, where the embedder starts
configuring a URLRequestContextBuilder, and the NetworkContext finishes
configuring it.

The reduces redundant code, lets us test the new path in production
before we ship the network service, and will allow Isolated App
URLRequestContexts to need less code when they're updated to use the
hybrid configuration path (Which I plan to do in a followup CL).

The NetworkContext constructor that takes an already-initialized
URLRequestContext is not modified in this CL.

Bug: 789644
Cq-Include-Trybots: luci.chromium.try:linux_mojo
Change-Id: Ibf40ae6497e7be06b0a666bc664ea943e145cae9
Reviewed-on: https://chromium-review.googlesource.com/1152083
Reviewed-by: Maks Orlovich <morlovich@chromium.org>
Reviewed-by: Clark DuVall <cduvall@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578740}
8 files changed