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

pkg/compiler/lib/src/resolution/resolution.dart

 // Copyright (c) 2012, 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 dart2js.resolution;
 
 import 'dart:collection' show Queue;
 
+import '../common.dart';
 import '../common/names.dart' show
     Identifiers;
 import '../common/resolution.dart' show
     Parsing,
     Resolution,
     ResolutionWorldImpact;
 import '../common/tasks.dart' show
     CompilerTask,
     DeferredAction;
 import '../compiler.dart' show
     Compiler;
 import '../compile_time_constants.dart' show
     ConstantCompiler;
 import '../constants/values.dart' show
     ConstantValue;
 import '../dart_types.dart';
-import '../diagnostics/diagnostic_listener.dart' show
-    DiagnosticMessage,
-    DiagnosticReporter;
-import '../diagnostics/invariant.dart' show
-    invariant;
-import '../diagnostics/messages.dart' show
-    MessageKind;
-import '../diagnostics/spannable.dart' show
-    Spannable;
 import '../elements/elements.dart';
 import '../elements/modelx.dart' show
     BaseClassElementX,
     BaseFunctionElementX,
     ConstructorElementX,
     FieldElementX,
     FunctionElementX,
     GetterElementX,
     MetadataAnnotationX,
     MixinApplicationElementX,
@@ skipping 1032 matching lines @@
   TreeElements get treeElements {
     assert(invariant(this, _treeElements !=null,
         message: "TreeElements have not been computed for $this."));
     return _treeElements;
   }
 
   void reuseElement() {
     _treeElements = null;
   }
 }