This unblocks removal of SkGLContext and its subclasses from the Skia lib. Using the null GrGLInterface here used to be problematic because its implementation stored its state globally, assuming there was only one instance. This is no longer the case.
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
Review URL: https://codereview.chromium.org/1829363003
Cr-Commit-Position: refs/heads/master@{#383375}