Reapply "Refactor constant part." (r4958) with fixes.

tests/language/src/CompileTimeConstant9Test.dart

Index: tests/language/src/CompileTimeConstant9Test.dart
diff --git a/tests/language/src/CompileTimeConstant9Test.dart b/tests/language/src/CompileTimeConstant9Test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..a149c43f11c1b94efb802fbad0ac84b423695504
--- /dev/null
+++ b/tests/language/src/CompileTimeConstant9Test.dart
@@ -0,0 +1,16 @@
+// 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 B {
+  const B();
+}
+
+class A {
+  var x = const B();
+  A();
+}
+
+main() {
+  Expect.isTrue(new A().x === new A().x);
+}