Make identical(a,b) a compile-time constant in dart2js.

tests/compiler/dart2js/mock_compiler.dart

Index: tests/compiler/dart2js/mock_compiler.dart
diff --git a/tests/compiler/dart2js/mock_compiler.dart b/tests/compiler/dart2js/mock_compiler.dart
index a1ac9a088c79798221aa291a1e97a5bdade7039c..14a90edc6aae7c78b0a3bb03e7ea1328a046aabf 100644
--- a/tests/compiler/dart2js/mock_compiler.dart
+++ b/tests/compiler/dart2js/mock_compiler.dart
@@ -64,7 +64,8 @@ const String DEFAULT_CORELIB = r'''
   class List {}
   class Closure {}
   class Null {}
-  class Dynamic_ {}''';
+  class Dynamic_ {}
+  bool identical(Object a, Object b) {}''';
 
 class MockCompiler extends Compiler {
   List<WarningMessage> warnings;