Add GrShaderFlags enum

Replaces GrGLSLUniformHandler::ShaderVisibility with GrShaderFlags.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1684063006

Review URL: https://codereview.chromium.org/1684063006
diff --git a/src/core/SkColorMatrixFilterRowMajor255.cpp b/src/core/SkColorMatrixFilterRowMajor255.cpp
index 33bf042..3b79d7f 100644
--- a/src/core/SkColorMatrixFilterRowMajor255.cpp
+++ b/src/core/SkColorMatrixFilterRowMajor255.cpp
@@ -257,10 +257,10 @@
 
         void emitCode(EmitArgs& args) override {
             GrGLSLUniformHandler* uniformHandler = args.fUniformHandler;
-            fMatrixHandle = uniformHandler->addUniform(GrGLSLUniformHandler::kFragment_Visibility,
+            fMatrixHandle = uniformHandler->addUniform(kFragment_GrShaderFlag,
                                                        kMat44f_GrSLType, kDefault_GrSLPrecision,
                                                        "ColorMatrix");
-            fVectorHandle = uniformHandler->addUniform(GrGLSLUniformHandler::kFragment_Visibility,
+            fVectorHandle = uniformHandler->addUniform(kFragment_GrShaderFlag,
                                                        kVec4f_GrSLType, kDefault_GrSLPrecision,
                                                        "ColorMatrixVector");