Make classes that own NetworkContextPtr also cache URLLoaderFactories.

Consumers in the browser process can now get a URLLoaderFactory* from
the StoragePartition or SystemNetworkContextManager to issue requests,
instead of having to create their own from a NetworkContext.

Bug: 770854
Change-Id: I3d33e36626f250386d0648853b2b38e10fe607b4
Reviewed-on: https://chromium-review.googlesource.com/696062
Commit-Queue: Matt Menke <mmenke@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#506096}
9 files changed