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/gradients/SkTwoPointConicalGradient_gpu.cpp b/src/effects/gradients/SkTwoPointConicalGradient_gpu.cpp
index ac32e72..b89f88a 100644
--- a/src/effects/gradients/SkTwoPointConicalGradient_gpu.cpp
+++ b/src/effects/gradients/SkTwoPointConicalGradient_gpu.cpp
@@ -227,7 +227,7 @@
     const Edge2PtConicalEffect& ge = args.fFp.cast<Edge2PtConicalEffect>();
     GrGLSLUniformHandler* uniformHandler = args.fUniformHandler;
     this->emitUniforms(uniformHandler, ge);
-    fParamUni = uniformHandler->addUniformArray(GrGLSLUniformHandler::kFragment_Visibility,
+    fParamUni = uniformHandler->addUniformArray(kFragment_GrShaderFlag,
                                                 kFloat_GrSLType, kDefault_GrSLPrecision,
                                                 "Conical2FSParams", 3);
 
@@ -510,7 +510,7 @@
     const FocalOutside2PtConicalEffect& ge = args.fFp.cast<FocalOutside2PtConicalEffect>();
     GrGLSLUniformHandler* uniformHandler = args.fUniformHandler;
     this->emitUniforms(uniformHandler, ge);
-    fParamUni = uniformHandler->addUniformArray(GrGLSLUniformHandler::kFragment_Visibility,
+    fParamUni = uniformHandler->addUniformArray(kFragment_GrShaderFlag,
                                                 kFloat_GrSLType, kDefault_GrSLPrecision,
                                                 "Conical2FSParams", 2);
     SkString tName("t");
@@ -720,7 +720,7 @@
     const FocalInside2PtConicalEffect& ge = args.fFp.cast<FocalInside2PtConicalEffect>();
     GrGLSLUniformHandler* uniformHandler = args.fUniformHandler;
     this->emitUniforms(uniformHandler, ge);
-    fFocalUni = uniformHandler->addUniform(GrGLSLUniformHandler::kFragment_Visibility,
+    fFocalUni = uniformHandler->addUniform(kFragment_GrShaderFlag,
                                            kFloat_GrSLType, kDefault_GrSLPrecision,
                                            "Conical2FSParams");
     SkString tName("t");
@@ -972,10 +972,10 @@
     const CircleInside2PtConicalEffect& ge = args.fFp.cast<CircleInside2PtConicalEffect>();
     GrGLSLUniformHandler* uniformHandler = args.fUniformHandler;
     this->emitUniforms(uniformHandler, ge);
-    fCenterUni = uniformHandler->addUniform(GrGLSLUniformHandler::kFragment_Visibility,
+    fCenterUni = uniformHandler->addUniform(kFragment_GrShaderFlag,
                                             kVec2f_GrSLType, kDefault_GrSLPrecision,
                                             "Conical2FSCenter");
-    fParamUni = uniformHandler->addUniform(GrGLSLUniformHandler::kFragment_Visibility,
+    fParamUni = uniformHandler->addUniform(kFragment_GrShaderFlag,
                                            kVec3f_GrSLType, kDefault_GrSLPrecision,
                                            "Conical2FSParams");
     SkString tName("t");
@@ -1209,10 +1209,10 @@
     const CircleOutside2PtConicalEffect& ge = args.fFp.cast<CircleOutside2PtConicalEffect>();
     GrGLSLUniformHandler* uniformHandler = args.fUniformHandler;
     this->emitUniforms(uniformHandler, ge);
-    fCenterUni = uniformHandler->addUniform(GrGLSLUniformHandler::kFragment_Visibility,
+    fCenterUni = uniformHandler->addUniform(kFragment_GrShaderFlag,
                                             kVec2f_GrSLType, kDefault_GrSLPrecision,
                                             "Conical2FSCenter");
-    fParamUni = uniformHandler->addUniform(GrGLSLUniformHandler::kFragment_Visibility,
+    fParamUni = uniformHandler->addUniform(kFragment_GrShaderFlag,
                                            kVec4f_GrSLType, kDefault_GrSLPrecision,
                                            "Conical2FSParams");
     SkString tName("t");