re-re-land of skslc now automatically turns on derivatives support

src/gpu/gl/builders/GrGLShaderStringBuilder.cpp

Index: src/gpu/gl/builders/GrGLShaderStringBuilder.cpp
diff --git a/src/gpu/gl/builders/GrGLShaderStringBuilder.cpp b/src/gpu/gl/builders/GrGLShaderStringBuilder.cpp
index 8e8bb9a0fc15427c29795fd94f4b66cc833747e4..8a5b700a90630d55a2a99463fecefbfa579018b7 100644
--- a/src/gpu/gl/builders/GrGLShaderStringBuilder.cpp
+++ b/src/gpu/gl/builders/GrGLShaderStringBuilder.cpp
@@ -85,6 +85,10 @@ SkSL::GLCaps GrGLSkSLCapsForContext(const GrGLContext& context) {
     result.fIsCoreProfile = caps->isCoreProfile();
     result.fUsesPrecisionModifiers = glslCaps->usesPrecisionModifiers();
     result.fMustDeclareFragmentShaderOutput = glslCaps->mustDeclareFragmentShaderOutput();
+    result.fShaderDerivativeSupport = glslCaps->shaderDerivativeSupport();
+    if (result.fShaderDerivativeSupport && glslCaps->shaderDerivativeExtensionString()) {
+        result.fShaderDerivativeExtensionString = glslCaps->shaderDerivativeExtensionString();
+    }
     result.fCanUseMinAndAbsTogether = glslCaps->canUseMinAndAbsTogether();
     result.fMustForceNegatedAtanParamToFloat = glslCaps->mustForceNegatedAtanParamToFloat();
     return result;