cc: Do not refcount SkNullGLContext

Use SkNullGLContext with normal ownership semantics
instead of refcount semantics. This allows SkGLContext
to be changed from refcounted object to normally owned
object.

Also calls different, non-deprecated constructor for
the class.

BUG=skia:2992
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1556043009

Cr-Commit-Position: refs/heads/master@{#367596}
2 files changed