Refactor to simplify safe-browsing gethash cache.
Stop propagating cached gethash values to the database, as
mandated by protocol v2.3. The timing of the cache clear may not
be precisely what v2.3 requests.
Convert SBFullHashResult.list_name to list_id, the name wasn't
needed. Remove add_chunk_id, it was not used.
Add SBFullHashCached to store cached and database hashes in memory.
BUG=172527
Review URL: https://codereview.chromium.org/
239743002
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@264432 0039d316-1c4b-4281-b951-d872f2087c98