Revert "eliminated GrGLSLExpr"

This reverts commit 93f20f5629e52eed732d2b9d6dbbb351cc30b2cd.

Reason for revert: Mismerge readded deleted files.

Original change's description:
> eliminated GrGLSLExpr
> 
> Now that skslc performs all of the optimizations (and then some) that
> GrGLSLExpr is responsible for, it's just extra work for no benefit.
> 
> Bug: skia:
> Change-Id: I40b0629e00a33873ed9fc6c0a9f41d8350221f9a
> Reviewed-on: https://skia-review.googlesource.com/14560
> Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> 

TBR=bsalomon@google.com,ethannicholas@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: Ia8b723594527afe34489fc78a4b49039081b6390
Reviewed-on: https://skia-review.googlesource.com/15154
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/src/gpu/effects/GrMatrixConvolutionEffect.cpp b/src/gpu/effects/GrMatrixConvolutionEffect.cpp
index b3ea81a..03d90ea 100644
--- a/src/gpu/effects/GrMatrixConvolutionEffect.cpp
+++ b/src/gpu/effects/GrMatrixConvolutionEffect.cpp
@@ -114,7 +114,10 @@
         fragBuilder->codeAppendf("%s.rgb = clamp(sum.rgb * %s + %s, 0, 1);", args.fOutputColor, gain, bias);
         fragBuilder->codeAppendf("%s.rgb *= %s.a;", args.fOutputColor, args.fOutputColor);
     }
-    fragBuilder->codeAppendf("%s *= %s;\n", args.fOutputColor, args.fInputColor);
+
+    SkString modulate;
+    GrGLSLMulVarBy4f(&modulate, args.fOutputColor, args.fInputColor);
+    fragBuilder->codeAppend(modulate.c_str());
 }
 
 void GrGLMatrixConvolutionEffect::GenKey(const GrProcessor& processor,