Delete the media cache(s) when using a single combined HTTP cache.

This is so that I can try increasing the media cache size in experiments
without increasing Chrome's profile size (Except possibly for profiles
that have never been used to play video).

Bug: 789657
Change-Id: I45e8f8c6e346a1fa7d05b0bea3e8b001d7dc41e1
Reviewed-on: https://chromium-review.googlesource.com/1130162
Reviewed-by: Maks Orlovich <morlovich@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574296}
2 files changed