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/gpu/effects/GrBezierEffect.cpp b/src/gpu/effects/GrBezierEffect.cpp
index fdb737d..2f378c3 100644
--- a/src/gpu/effects/GrBezierEffect.cpp
+++ b/src/gpu/effects/GrBezierEffect.cpp
@@ -215,12 +215,11 @@
     // TODO should we really be doing this?
     if (gp.coverageScale() != 0xff) {
         const char* coverageScale;
-        fCoverageScaleUniform = uniformHandler->addUniform(
-                                                         GrGLSLUniformHandler::kFragment_Visibility,
-                                                         kFloat_GrSLType,
-                                                         kHigh_GrSLPrecision,
-                                                         "Coverage",
-                                                         &coverageScale);
+        fCoverageScaleUniform = uniformHandler->addUniform(kFragment_GrShaderFlag,
+                                                           kFloat_GrSLType,
+                                                           kHigh_GrSLPrecision,
+                                                           "Coverage",
+                                                           &coverageScale);
         fragBuilder->codeAppendf("%s = vec4(%s * %s);",
                                  args.fOutputCoverage, coverageScale, edgeAlpha.c_str());
     } else {
@@ -433,12 +432,11 @@
 
     if (0xff != gp.coverageScale()) {
         const char* coverageScale;
-        fCoverageScaleUniform = uniformHandler->addUniform(
-                                                         GrGLSLUniformHandler::kFragment_Visibility,
-                                                         kFloat_GrSLType,
-                                                         kDefault_GrSLPrecision,
-                                                         "Coverage",
-                                                         &coverageScale);
+        fCoverageScaleUniform = uniformHandler->addUniform(kFragment_GrShaderFlag,
+                                                           kFloat_GrSLType,
+                                                           kDefault_GrSLPrecision,
+                                                           "Coverage",
+                                                           &coverageScale);
         fragBuilder->codeAppendf("%s = vec4(%s * edgeAlpha);", args.fOutputCoverage, coverageScale);
     } else {
         fragBuilder->codeAppendf("%s = vec4(edgeAlpha);", args.fOutputCoverage);