Re-land of "eliminated GrGLSLExpr".


This change is exactly the same as the last time it was landed; I believe the
underlying optimizer bug that was causing this to cause problems has been
fixed by a prior CL.
Bug: skia:
Change-Id: I5436422f094ea758caa3cd69e9338db31b1f93fa
Reviewed-on: https://skia-review.googlesource.com/15768
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
29 files changed