Add ShaderBuilders to EmitArgs and remove gettings from ProgBuilder.

BUG=skia:

Review URL: https://codereview.chromium.org/1457543003
diff --git a/src/gpu/glsl/GrGLSLPrimitiveProcessor.cpp b/src/gpu/glsl/GrGLSLPrimitiveProcessor.cpp
index abb3abc..70b58cd 100644
--- a/src/gpu/glsl/GrGLSLPrimitiveProcessor.cpp
+++ b/src/gpu/glsl/GrGLSLPrimitiveProcessor.cpp
@@ -33,9 +33,9 @@
 }
 
 void GrGLSLPrimitiveProcessor::setupUniformColor(GrGLSLGPBuilder* pb,
+                                                 GrGLSLFragmentBuilder* fragBuilder,
                                                  const char* outputName,
                                                  UniformHandle* colorUniform) {
-    GrGLSLFragmentBuilder* fs = pb->getFragmentShaderBuilder();
     SkASSERT(colorUniform);
     const char* stagedLocalVarName;
     *colorUniform = pb->addUniform(GrGLSLProgramBuilder::kFragment_Visibility,
@@ -43,5 +43,5 @@
                                    kDefault_GrSLPrecision,
                                    "Color",
                                    &stagedLocalVarName);
-    fs->codeAppendf("%s = %s;", outputName, stagedLocalVarName);
+    fragBuilder->codeAppendf("%s = %s;", outputName, stagedLocalVarName);
 }