Add mjsunit test for the overriding of read-only properties....

test/mjsunit/override-read-only-property.js

Index: test/mjsunit/override-read-only-property.js
===================================================================
--- test/mjsunit/override-read-only-property.js	(revision 0)
+++ test/mjsunit/override-read-only-property.js	(revision 0)
@@ -0,0 +1,64 @@
+// Copyright 2009 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// According to ECMA-262, sections 8.6.2.2 and 8.6.2.3 you're not
+// allowed to override read-only properties, not even if the read-only
+// property is in the prototype chain.
+//
+// However, for compatibility with WebKit/JSC, we allow the overriding
+// of read-only properties in prototype chains.
+
+function F() {};
+F.prototype = Number;
+
+var original_number_max = Number.MAX_VALUE;
+
+// Assignment to a property which does not exist on the object itself,
+// but is read-only in a prototype takes effect.
+var f = new F();
+assertEquals(original_number_max, f.MAX_VALUE);
+f.MAX_VALUE = 42;
+assertEquals(42, f.MAX_VALUE);
+
+// Assignment to a property which does not exist on the object itself,
+// but is read-only in a prototype takes effect.
+f = new F();
+with (f) {
+  MAX_VALUE = 42;
+}
+assertEquals(42, f.MAX_VALUE);
+
+// Assignment to read-only property on the object itself is ignored.
+Number.MAX_VALUE = 42;
+assertEquals(original_number_max, Number.MAX_VALUE);
+
+// G should be read-only on the global object and the assignment is
+// ignored.
+(function G() {
+  eval("G = 42;");
+  assertTrue(typeof G === 'function');
+})();