Add test case for issue 2793 about experimental natives.

test/mjsunit/harmony/collections.js

Index: test/mjsunit/harmony/collections.js
diff --git a/test/mjsunit/harmony/collections.js b/test/mjsunit/harmony/collections.js
index 67f91a8ad4a75f561771742b70565a490f52aa97..3e87e6b533bdea945ea775e1c625ce8ec912d185 100644
--- a/test/mjsunit/harmony/collections.js
+++ b/test/mjsunit/harmony/collections.js
@@ -288,6 +288,22 @@ assertEquals("WeakMap", WeakMap.name);
 assertEquals("WeakSet", WeakSet.name);
 
 
+// Test prototype property of Set, Map, WeakMap and WeakSet.
+function TestPrototype(C) {
+  assertTrue(C.prototype instanceof Object);
+  assertEquals({
+    value: {},
+    writable: true,  // TODO(2793): This should be non-writable.
+    enumerable: false,
+    configurable: false
+  }, Object.getOwnPropertyDescriptor(C, "prototype"));
+}
+TestPrototype(Set);
+TestPrototype(Map);
+TestPrototype(WeakMap);
+TestPrototype(WeakSet);
+
+
 // Test constructor property of the Set, Map, WeakMap and WeakSet prototype.
 function TestConstructor(C) {
   assertFalse(C === Object.prototype.constructor);
@@ -301,6 +317,7 @@ TestConstructor(WeakMap);
 TestConstructor(WeakSet);
 
 
+// Test the Set, Map, WeakMap and WeakSet global properties themselves.
 function TestDescriptor(global, C) {
   assertEquals({
     value: C,