Add flag bits for partial GrContext reset

BUG=248728
R=bsalomon@google.com

Review URL: https://codereview.chromium.org/17027003

git-svn-id: http://skia.googlecode.com/svn/trunk@9802 2bbb7eff-a529-9590-31e7-b0007b416f81
6 files changed