added SkSL support for mustForceNegatedAtanParamToFloat cap

tests/SkSLGLSLTest.cpp

Index: tests/SkSLGLSLTest.cpp
diff --git a/tests/SkSLGLSLTest.cpp b/tests/SkSLGLSLTest.cpp
index dedddad1f8a6a9ce07daebcf15e33d4f61227256..b615f678140ecca0de5a7b38a1273a4cb1a5ba99 100644
--- a/tests/SkSLGLSLTest.cpp
+++ b/tests/SkSLGLSLTest.cpp
@@ -33,7 +33,8 @@ static SkSL::GLCaps default_caps() {
              false, // isCoreProfile
              false, // usesPrecisionModifiers;
              false, // mustDeclareFragmentShaderOutput
-             true   // canUseMinAndAbsTogether
+             true,  // canUseMinAndAbsTogether
+             false  // mustForceNegatedAtanParamToFloat
            };
 }
 
@@ -315,6 +316,27 @@ DEF_TEST(SkSLMinAbs, r) {
          "}\n");
 }
 
+DEF_TEST(SkSLNegatedAtan, r) {
+    test(r,
+         "void main() { vec2 x = vec2(1, 2); float y = atan(x.x, -(2 * x.y)); }",
+         default_caps(),
+         "#version 400\n"
+         "void main() {\n"
+         "    vec2 x = vec2(1.0, 2.0);\n"
+         "    float y = atan(x.x, -(2.0 * x.y));\n"
+         "}\n");
+    SkSL::GLCaps caps = default_caps();
+    caps.fMustForceNegatedAtanParamToFloat = true;
+    test(r,
+         "void main() { vec2 x = vec2(1, 2); float y = atan(x.x, -(2 * x.y)); }",
+         caps,
+         "#version 400\n"
+         "void main() {\n"
+         "    vec2 x = vec2(1.0, 2.0);\n"
+         "    float y = atan(x.x, -1.0 * (2.0 * x.y));\n"
+         "}\n");
+}
+
 DEF_TEST(SkSLModifiersDeclaration, r) {
     test(r,
          "layout(blend_support_all_equations) out;"