Add ShaderBuilders to EmitArgs and remove gettings from ProgBuilder.

BUG=skia:

Review URL: https://codereview.chromium.org/1457543003
diff --git a/experimental/SkPerlinNoiseShader2/SkPerlinNoiseShader2.cpp b/experimental/SkPerlinNoiseShader2/SkPerlinNoiseShader2.cpp
index eff451a..83599d9 100644
--- a/experimental/SkPerlinNoiseShader2/SkPerlinNoiseShader2.cpp
+++ b/experimental/SkPerlinNoiseShader2/SkPerlinNoiseShader2.cpp
@@ -757,7 +757,7 @@
 }
 
 void GrGLPerlinNoise2::emitCode(EmitArgs& args) {
-    GrGLSLFragmentBuilder* fsBuilder = args.fBuilder->getFragmentShaderBuilder();
+    GrGLSLFragmentBuilder* fsBuilder = args.fFragBuilder;
     SkString vCoords = fsBuilder->ensureFSCoords2D(args.fCoords, 0);
 
     fBaseFrequencyUni = args.fBuilder->addUniform(GrGLSLProgramBuilder::kFragment_Visibility,
@@ -1170,7 +1170,7 @@
 }
 
 void GrGLImprovedPerlinNoise::emitCode(EmitArgs& args) {
-    GrGLSLFragmentBuilder* fsBuilder = args.fBuilder->getFragmentShaderBuilder();
+    GrGLSLFragmentBuilder* fsBuilder = args.fFragBuilder;
     SkString vCoords = fsBuilder->ensureFSCoords2D(args.fCoords, 0);
 
     fBaseFrequencyUni = args.fBuilder->addUniform(GrGLSLProgramBuilder::kFragment_Visibility,