more c

BUG=skia:
TBR=

Review URL: https://codereview.chromium.org/736133006
free up picturerecorder refs after returning picture or drawable

this just accelerates what would happen on the next beginRecording() call or the destructor. chrome has unittests that break (shaders on the stack) if we hold on to the internals past endRecording().

BUG=skia:
TBR=

Review URL: https://codereview.chromium.org/758813002