Add a missing SK_API to SkImageFilter::Cache.

TBR=bsalomon@google.com

Review URL: https://codereview.chromium.org/251353003

git-svn-id: http://skia.googlecode.com/svn/trunk@14343 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed