Add GrShaderFlags enum

Replaces GrGLSLUniformHandler::ShaderVisibility with GrShaderFlags.

BUG=skia:
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Review URL: https://codereview.chromium.org/1684063006
diff --git a/src/gpu/glsl/GrGLSLGeometryProcessor.cpp b/src/gpu/glsl/GrGLSLGeometryProcessor.cpp
index 967c18d..b8951be 100644
--- a/src/gpu/glsl/GrGLSLGeometryProcessor.cpp
+++ b/src/gpu/glsl/GrGLSLGeometryProcessor.cpp
@@ -50,7 +50,7 @@
 
             const char* uniName;
             fInstalledTransforms[i][t].fHandle =
-                    uniformHandler->addUniform(GrGLSLUniformHandler::kVertex_Visibility,
+                    uniformHandler->addUniform(kVertex_GrShaderFlag,
                                                kMat33f_GrSLType, precision,
                                                strUniName.c_str(),
                                                &uniName).toIndex();
@@ -139,7 +139,7 @@
         vertBuilder->codeAppendf("vec2 %s = %s;", gpArgs->fPositionVar.c_str(), posName);
     } else {
         const char* viewMatrixName;
-        *viewMatrixUniform = uniformHandler->addUniform(GrGLSLUniformHandler::kVertex_Visibility,
+        *viewMatrixUniform = uniformHandler->addUniform(kVertex_GrShaderFlag,
                                                         kMat33f_GrSLType, kHigh_GrSLPrecision,
                                                         "uViewM",
                                                         &viewMatrixName);