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

tests/SkSLGLSLTest.cpp

Index: tests/SkSLGLSLTest.cpp
diff --git a/tests/SkSLGLSLTest.cpp b/tests/SkSLGLSLTest.cpp
index b615f678140ecca0de5a7b38a1273a4cb1a5ba99..ad1fe0d9014671fc54ebafd1e93f229611d8caae 100644
--- a/tests/SkSLGLSLTest.cpp
+++ b/tests/SkSLGLSLTest.cpp
@@ -27,15 +27,7 @@ static void test(skiatest::Reporter* r, const char* src, SkSL::GLCaps caps, cons
 }
 
 static SkSL::GLCaps default_caps() {
-    return { 
-             400, 
-             SkSL::GLCaps::kGL_Standard,
-             false, // isCoreProfile
-             false, // usesPrecisionModifiers;
-             false, // mustDeclareFragmentShaderOutput
-             true,  // canUseMinAndAbsTogether
-             false  // mustForceNegatedAtanParamToFloat
-           };
+    return SkSL::GLCaps();
 }
 
 DEF_TEST(SkSLHelloWorld, r) {
@@ -387,3 +379,30 @@ DEF_TEST(SkSLArrayConstructors, r) {
          "vec2 test2[] = vec2[](vec2(1.0, 2.0), vec2(3.0, 4.0));\n"
          "mat4 test3[] = mat4[]();\n");
 }
+
+DEF_TEST(SkSLDerivatives, r) {
+    test(r,
+         "void main() { float x = dFdx(1); }",
+         default_caps(),
+         "#version 400\n"
+         "void main() {\n"
+         "    float x = dFdx(1.0);\n"
+         "}\n");
+    SkSL::GLCaps caps = default_caps();
+    caps.fShaderDerivativeExtensionString = "GL_OES_standard_derivatives";
+    test(r,
+         "void main() { float x = 1; }",
+         caps,
+         "#version 400\n"
+         "void main() {\n"
+         "    float x = 1.0;\n"
+         "}\n");
+    test(r,
+         "void main() { float x = dFdx(1); }",
+         caps,
+         "#version 400\n"
+         "#extension GL_OES_standard_derivatives : require\n"
+         "void main() {\n"
+         "    float x = dFdx(1.0);\n"
+         "}\n");
+}