Use common.dart to re-export commonly used entities.

pkg/compiler/lib/src/ordered_typeset.dart

Index: pkg/compiler/lib/src/ordered_typeset.dart
diff --git a/pkg/compiler/lib/src/ordered_typeset.dart b/pkg/compiler/lib/src/ordered_typeset.dart
index 290b94fbc8e1542c4865d2b126421fe7fbb24bf6..a5da246c2e7ce4f6c24239c6a200768cba4d5a60 100644
--- a/pkg/compiler/lib/src/ordered_typeset.dart
+++ b/pkg/compiler/lib/src/ordered_typeset.dart
@@ -4,15 +4,10 @@
 
 library ordered_typeset;
 
+import 'common.dart';
 import 'compiler.dart' show
     Compiler;
 import 'dart_types.dart';
-import 'diagnostics/diagnostic_listener.dart' show
-    DiagnosticReporter;
-import 'diagnostics/invariant.dart' show
-    invariant;
-import 'diagnostics/messages.dart' show
-    MessageKind;
 import 'elements/elements.dart' show
     ClassElement;
 import 'util/util.dart' show