Implement code generation for === and !==.

frog/tests/leg/src/IdentityTest.dart

+// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#import("compiler_helper.dart");
+
+final String TEST_ONE = @"""
+class A {}
+bool foo(bar) {
+  var x = new A();
+  var y = new A();
+  return x === y;
+}
+""";
+
+main() {
+  String generated = compile(TEST_ONE, 'foo');
+
+  // Check that no boolify code is generated.
+  RegExp regexp = const RegExp("=== true");
+  Iterator matches = regexp.allMatches(generated).iterator();
+  Expect.isFalse(matches.hasNext());
+
+  regexp = const RegExp("===");
+  matches = regexp.allMatches(generated).iterator();

[ngeoffray, 2012/01/06 08:10:20]

There is a checkNumberOfMatches method in TypeGuardUnuserTest that could be
shared.

+  Expect.isTrue(matches.hasNext());
+  matches.next();
+  Expect.isFalse(matches.hasNext());
+}