Add a CanonicalizedMap class to pkg/collection.

pkg/collection/lib/src/utils.dart

Index: pkg/collection/lib/src/utils.dart
diff --git a/tests/language/metadata_self_test.dart b/pkg/collection/lib/src/utils.dart
similarity index 63%
copy from tests/language/metadata_self_test.dart
copy to pkg/collection/lib/src/utils.dart
index 434cc38a0a0c2cc3aa81953b34b4cbdb7cd8abee..c9c753777f07c1c5bd930fa4a3a7e32a5377db0f 100644
--- a/tests/language/metadata_self_test.dart
+++ b/pkg/collection/lib/src/utils.dart
@@ -2,13 +2,12 @@
 // 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.
 
-// Test that metadata refer to the annotated declaration.
+library dart.pkg.collection.utils;
 
-@Foo()
-class Foo {
-  const Foo();
-}
+/// A pair of values.
+class Pair<E, F> {
+  E first;
+  F last;
 
-main() {
-  Foo f = const Foo();
+  Pair(this.first, this.last);
 }