[builtins] Implement Array.prototype.reduce in the CSA

test/mjsunit/array-reduce.js

Index: test/mjsunit/array-reduce.js
diff --git a/test/mjsunit/array-reduce.js b/test/mjsunit/array-reduce.js
index 94e51440b154edb6dc2a6ae9f2b0cf10ca2f9343..f34d3ef6ff2439c412501af9457ef03ccab5355e 100644
--- a/test/mjsunit/array-reduce.js
+++ b/test/mjsunit/array-reduce.js
@@ -408,6 +408,12 @@ testReduce("reduceRight", "ArrayWithNonElementPropertiesReduceRight", 6,
             [5, 1, 0, arrayPlus, 6],
            ], arrayPlus, sum, 0);
 
+// Test passing undefined as initial value (to test missing parameter
+// detection).
+[1].reduce((a, b) => { assertEquals(a, undefined); assertEquals(b, 1) },
+           undefined);
+[1, 2].reduce((a, b) => { assertEquals(a, 1); assertEquals(b, 2); });
+[1].reduce((a, b) => { assertTrue(false); });
 
 // Test error conditions: