Cover an example of equality and hashCode for each type of mirror.

runtime/lib/mirrors_impl.dart

Index: runtime/lib/mirrors_impl.dart
diff --git a/runtime/lib/mirrors_impl.dart b/runtime/lib/mirrors_impl.dart
index b8fb3f9ca00511caa07e487461dc778d8c4c99a3..61bd05b6aa82529f0f2b384dba8b0b95d60a42c0 100644
--- a/runtime/lib/mirrors_impl.dart
+++ b/runtime/lib/mirrors_impl.dart
@@ -139,10 +139,6 @@ class _LocalMirrorSystemImpl extends MirrorSystem {
 }
 
 abstract class _LocalMirrorImpl implements Mirror {
-  int get hashCode {
-    throw new UnimplementedError('Mirror.hashCode is not implemented');
-  }
-
   // Local mirrors always return the same MirrorSystem.  This field
   // is more interesting once we implement remote mirrors.
   MirrorSystem get mirrors => _Mirrors.currentMirrorSystem();