Move context types into STAGE() macros.

This is something I came up with while writing _lowp.cpp.

This should all be a logical no-op, but there are some code generation
changes.  I'm not exactly sure why.

Change-Id: Iaad36b5298b37fe26ebd375a147a48852f98e1e4
Reviewed-on: https://skia-review.googlesource.com/52003
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Herb Derby <herb@google.com>
4 files changed