Protect against unref/ref of stencil buffer.
Protect against unref/ref of stencil buffer.


Over the shoulder review from robertphillips@google.com



git-svn-id: e8541e15acce502a64c929015570ad1648e548cd@6476 2bbb7eff-a529-9590-31e7-b0007b416f81

Cue/skia,Cue/skia,Cue/skia,Cue/skia