Fix bug where constants were not correctly canonicalized.

tests/language/src/CompileTimeConstantMTest.dart

Index: tests/language/src/CompileTimeConstantMTest.dart
diff --git a/tests/language/src/CompileTimeConstantMTest.dart b/tests/language/src/CompileTimeConstantMTest.dart
new file mode 100644
index 0000000000000000000000000000000000000000..f570ec0feda68424de613f980fc1e24020248ef6
--- /dev/null
+++ b/tests/language/src/CompileTimeConstantMTest.dart
@@ -0,0 +1,17 @@
+// Copyright (c) 2012, 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.
+
+class A {
+  const A();
+  foo([x = const A()]) => x;
+}
+
+final x = const A();
+
+foo([x = const A()]) => x;
+
+main() {
+  Expect.identical(x, foo());
+  Expect.identical(x, x.foo());
+}