Create a hash table from id<-->key in SkImageFilter::CacheImpl

There is memory leak in the SkImageFilter::Cache. There are two sources
of memory leak:
1. The cache filling up quickly.
2. A slow small leak that never stops.
This CL solves the first issue, which prevents the cache filling up quickly.
This CL creates a new hash table that index the
SkImageFilter::uniqueID to an array of keys, and with the existing
key<-->Value hash table, we can have SkImageFilters proactively
purge content derived cached content when destroyed.

BUG=489543
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1514893003

Committed: https://skia.googlesource.com/skia/+/f5d1f8dcc841516d7ea63c151b13059af40ca76d

Review URL: https://codereview.chromium.org/1514893003

0 files changed, 0 insertions, 0 deletions