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/effects/SkMorphologyImageFilter.cpp b/src/effects/SkMorphologyImageFilter.cpp
index bc5bdee..3657e33 100644
--- a/src/effects/SkMorphologyImageFilter.cpp
+++ b/src/effects/SkMorphologyImageFilter.cpp
@@ -271,11 +271,11 @@
     const GrMorphologyEffect& me = args.fFp.cast<GrMorphologyEffect>();
 
     GrGLSLUniformHandler* uniformHandler = args.fUniformHandler;
-    fPixelSizeUni = uniformHandler->addUniform(GrGLSLUniformHandler::kFragment_Visibility,
+    fPixelSizeUni = uniformHandler->addUniform(kFragment_GrShaderFlag,
                                                kFloat_GrSLType, kDefault_GrSLPrecision,
                                                "PixelSize");
     const char* pixelSizeInc = uniformHandler->getUniformCStr(fPixelSizeUni);
-    fRangeUni = uniformHandler->addUniform(GrGLSLUniformHandler::kFragment_Visibility,
+    fRangeUni = uniformHandler->addUniform(kFragment_GrShaderFlag,
                                            kVec2f_GrSLType, kDefault_GrSLPrecision,
                                            "Range");
     const char* range = uniformHandler->getUniformCStr(fRangeUni);