added SkSL support for mustForceNegatedAtanParamToFloat cap

src/sksl/SkSLMain.cpp

Index: src/sksl/SkSLMain.cpp
diff --git a/src/sksl/SkSLMain.cpp b/src/sksl/SkSLMain.cpp
index de1b9819d55a5bc7f59c909de451b49cb392cd40..fe925e0c6e2c42c1febeef74d3df4619a22dfb64 100644
--- a/src/sksl/SkSLMain.cpp
+++ b/src/sksl/SkSLMain.cpp
@@ -23,7 +23,8 @@ static SkSL::GLCaps default_caps() {
              false, // isCoreProfile
              false, // usesPrecisionModifiers;
              false, // mustDeclareFragmentShaderOutput
-             true   // canUseMinAndAbsTogether
+             true,  // canUseMinAndAbsTogether
+             false  // mustForceNegatedAtanParamToFloat
            };
 }