Revert "Revert of remove unused SkCachingPixelRef (patchset #1 id:1 of https://codereview.chromium.org/1364743002/ )"

removed test for unsupported SkInstallDiscardable...

This reverts commit 60c73d51808b9d78f65381b83f628a3f523042fe.

BUG=skia:
TBR=

Review URL: https://codereview.chromium.org/1369443002
4 files changed