Restore untrusted glStencilMask value on resume after functor

Fixes an issue where the stencil buffer is corrupted
(used in overdraw debugging, path clipping) when used in
conjunction with a HW accelerated WebView.

bug:15023700
bug:16465551

Change-Id: If201b503931380f7107a34e9a9a2f877a50f72b1