Make GrGLShaderBuilder responsible for enabling GLSL extensions

src/gpu/effects/GrEdgeEffect.cpp

Index: src/gpu/effects/GrEdgeEffect.cpp
===================================================================
--- src/gpu/effects/GrEdgeEffect.cpp	(revision 8458)
+++ src/gpu/effects/GrEdgeEffect.cpp	(working copy)
@@ -38,7 +38,7 @@
             builder->fsCodeAppendf("\t\tedgeAlpha = max(1.0 - edgeAlpha, 0.0);\n");
             break;
         case GrEdgeEffect::kQuad_EdgeType:
-            GrAssert(builder->ctxInfo().caps()->shaderDerivativeSupport());
+            SkAssertResult(builder->enableFeature(GrGLShaderBuilder::kStandardDerivatives_GLSLFeature));
             builder->addVarying(kVec4f_GrSLType, "QuadEdge", &vsName, &fsName);
 
             // keep the derivative instructions outside the conditional
@@ -56,12 +56,9 @@
                                    fsName);
             builder->fsCodeAppendf("\t\t\tedgeAlpha = "
                                    "clamp(0.5 - edgeAlpha / length(gF), 0.0, 1.0);\n\t\t}\n");
-            if (kES2_GrGLBinding == builder->ctxInfo().binding()) {
-                builder->fHeader.append("#extension GL_OES_standard_derivatives: enable\n");
-            }
             break;
         case GrEdgeEffect::kHairQuad_EdgeType:
-            GrAssert(builder->ctxInfo().caps()->shaderDerivativeSupport());
+            SkAssertResult(builder->enableFeature(GrGLShaderBuilder::kStandardDerivatives_GLSLFeature));
             builder->addVarying(kVec4f_GrSLType, "HairQuadEdge", &vsName, &fsName);
 
             builder->fsCodeAppendf("\t\tvec2 duvdx = dFdx(%s.xy);\n", fsName);
@@ -73,9 +70,6 @@
                                    fsName);
             builder->fsCodeAppend("\t\tedgeAlpha = sqrt(edgeAlpha*edgeAlpha / dot(gF, gF));\n");
             builder->fsCodeAppend("\t\tedgeAlpha = max(1.0 - edgeAlpha, 0.0);\n");
-            if (kES2_GrGLBinding == builder->ctxInfo().binding()) {
-                builder->fHeader.append("#extension GL_OES_standard_derivatives: enable\n");
-            }
             break;
         };