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>
diff --git a/src/gpu/effects/GrXfermodeFragmentProcessor.cpp b/src/gpu/effects/GrXfermodeFragmentProcessor.cpp
index 30a9faa..aa79937 100644
--- a/src/gpu/effects/GrXfermodeFragmentProcessor.cpp
+++ b/src/gpu/effects/GrXfermodeFragmentProcessor.cpp
@@ -415,7 +415,7 @@
         ComposeOneFragmentProcessor::Child child =
             args.fFp.cast<ComposeOneFragmentProcessor>().child();
         SkString childColor("child");
-        this->emitChild(0, nullptr, &childColor, args);
+        this->emitChild(0, &childColor, args);
 
         const char* inputColor = args.fInputColor;
         // We don't try to optimize for this case at all