Make the ClassMirrors created through reflectClass() find their owners (libraries) lazily.

runtime/lib/mirrors_impl.dart

Index: runtime/lib/mirrors_impl.dart
===================================================================
--- runtime/lib/mirrors_impl.dart	(revision 25137)
+++ runtime/lib/mirrors_impl.dart	(working copy)
@@ -422,7 +422,10 @@
 
   var _owner;
   DeclarationMirror get owner {
-    if (_owner != null && _owner is! Mirror) {
+    if (_owner == null) {
+      _owner = _library(_reflectee);
+    }
+    if (_owner is! Mirror) {
       _owner = _owner.resolve(mirrors);
     }
     return _owner;
@@ -573,6 +576,9 @@
   static _name(reflectee)
       native "ClassMirror_name";
 
+  static _library(reflectee)
+      native "ClassMirror_library";
+
   _invoke(reflectee, memberName, positionalArguments)
       native 'ClassMirror_invoke';