retool image cache to be generic cache, allowing the client to subclass "Rec", so they can provide a custom Key and arbitrary Value.

Follow-on CLs

- rename ScaledimageCache to something like GeneralCache
- explore if we can use call-backs or some mechanism to completely hide "lock/unlock", by forcing all clients to support "copying" their value out of the cache as the result of a Find.

R=mtklein@google.com, senorblanco@google.com, bsalomon@google.com, qiankun.miao@intel.com, senorblanco@chromium.org

Author: reed@google.com

Review URL: https://codereview.chromium.org/507483002
11 files changed