Avoid caching resources for volatile bitmap shaders

SkBitmapProvider::isVolatile() treats all SkImages as non-volatile,
which is not what we want for temp SkImage wrappers of volatile bitmaps.

R=reed@google.com
BUG=chromium:633941
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2222783002

Review-Url: https://codereview.chromium.org/2222783002
1 file changed