Add an imported into list for libraries so that it is possible to lookup

vm/class_finalizer.cc

Index: vm/class_finalizer.cc
===================================================================
--- vm/class_finalizer.cc	(revision 591)
+++ vm/class_finalizer.cc	(working copy)
@@ -93,6 +93,13 @@
     }
     // Clear pending classes array.
     object_store->set_pending_classes(Array::Handle(Array::Empty()));
+
+    // Check to ensure there are no duplicate definitions in the library
+    // hierarchy.
+    const String& str = String::Handle(Library::CheckForDuplicateDefinition());
+    if (!str.IsNull()) {
+      ReportError("Duplicate definition : %s\n", str.ToCString());
+    }
   } else {
     retval = false;
   }