Refcount AppCacheGroup correctly.

TBR=palmer@chromium.org

(cherry picked from commit 9d2ead1650a1c901754dd1a68705006a6934cffc)

Bug: 888926
Change-Id: Iab0d82d272e2f24a5e91180d64bc8e2aa8a8238d
Reviewed-on: https://chromium-review.googlesource.com/1246827
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Reviewed-by: Joshua Bell <jsbell@chromium.org>
Commit-Queue: Chris Palmer <palmer@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#594475}
Reviewed-on: https://chromium-review.googlesource.com/1252004
Cr-Commit-Position: refs/branch-heads/3538@{#733}
Cr-Branched-From: 79f7c91a2b2a2932cd447fa6f865cb6662fa8fa6-refs/heads/master@{#587811}
1 file changed