Add support for atan() to DSL.

Change-Id: I00cc1e89fd85fdc0ce0860fcb35ececd0eaec50a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/400540
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
diff --git a/tests/SkSLDSLTest.cpp b/tests/SkSLDSLTest.cpp
index 43c82e4..9a2e35f 100644
--- a/tests/SkSLDSLTest.cpp
+++ b/tests/SkSLDSLTest.cpp
@@ -1435,6 +1435,8 @@
     EXPECT_EQUAL(Abs(a),                 "abs(a)");
     EXPECT_EQUAL(All(b4),                "all(b4)");
     EXPECT_EQUAL(Any(b4),                "any(b4)");
+    EXPECT_EQUAL(Atan(a),                "atan(a)");
+    EXPECT_EQUAL(Atan(a, b),             "atan(a, b)");
     EXPECT_EQUAL(Ceil(a),                "ceil(a)");
     EXPECT_EQUAL(Clamp(a, 0, 1),         "clamp(a, 0.0, 1.0)");
     EXPECT_EQUAL(Cos(a),                 "cos(a)");