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

pkg/compiler/lib/src/js_backend/codegen/glue.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // 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.
 
 library code_generator_dependencies;
 
 import '../js_backend.dart';
+
+import '../../common.dart';
 import '../../common/registry.dart' show
     Registry;
 import '../../common/codegen.dart' show
     CodegenRegistry;
 import '../../compiler.dart' show
     Compiler;
 import '../../constants/values.dart';
 import '../../dart_types.dart' show
     DartType,
     TypeVariableType,
     InterfaceType;
-import '../../diagnostics/diagnostic_listener.dart' show
-    DiagnosticReporter;
-import '../../diagnostics/spannable.dart' show
-    CURRENT_ELEMENT_SPANNABLE;
 import '../../enqueue.dart' show
     CodegenEnqueuer;
 import '../../elements/elements.dart';
 import '../../js_emitter/js_emitter.dart';
 import '../../js/js.dart' as js;
 import '../../native/native.dart' show NativeBehavior;
 import '../../universe/selector.dart' show
     Selector;
 import '../../world.dart' show
     ClassWorld;
@@ skipping 254 matching lines @@
   bool isBoolClass(ClassElement classElement) =>
       classElement == _backend.jsBoolClass ||
       classElement == _compiler.boolClass;
 
   // TODO(sra): Should this be part of CodegenRegistry?
   void registerNativeBehavior(NativeBehavior nativeBehavior, node) {
     if (nativeBehavior == null) return;
     _enqueuer.nativeEnqueuer.registerNativeBehavior(nativeBehavior, node);
   }
 }