Add an experimental "feature" to disable the media cache.

When enabled, a Profile's media URLRequestContext will just use the
same disk cache as the main one. Also affect App Media
URLRequestContexts.

Bug: 789657
Change-Id: I4150324ad84c1679495bd512dd0231edb30c733b
Reviewed-on: https://chromium-review.googlesource.com/1064858
Reviewed-by: Maks Orlovich <morlovich@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#559712}
4 files changed