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

lib/core/object.dart

Index: lib/core/object.dart
diff --git a/lib/core/object.dart b/lib/core/object.dart
index 7febc393e5de13dd3b615ca8f80375a392ec25a6..2506d1777e086474cb7fce3b1877830dc15b525a 100644
--- a/lib/core/object.dart
+++ b/lib/core/object.dart
@@ -8,7 +8,7 @@
 class Object {
   const Object();
 
-  bool operator ==(other) => this === other;
+  bool operator ==(other) => identical(this, other);
 
   get dynamic => this;
 
@@ -16,3 +16,8 @@ class Object {
 
   external void noSuchMethod(String name, List args);
 }
+
+/**
+ * Check whether two references are to the same object.
+ */
+bool identical(Object a, Object b) => a === b;