Refactor location computation in dart2js mirrors.

sdk/lib/_internal/compiler/implementation/elements/elements.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 elements;
 
 import 'dart:uri';
 
 // TODO(ahe): Rename prefix to 'api' when VM bug is fixed.
 import '../../compiler.dart' as api_e;
@@ skipping 2143 matching lines @@
  */
 abstract class MetadataAnnotation {
   /**
    * The compile-time constant which this annotation resolves to.
    * In the mirror system, this would be an object mirror.
    */
   Constant get value;
   Element annotatedElement;
   int resolutionState;
 
+  /**
+   * The beginning token of this annotation, or [:null:] if it is synthetic.
+   */
+  Token get beginToken;
+

[Johnni Winther, 2013/01/04 09:57:56]

Needed in this CL and not in https://codereview.chromium.org/11726005/

   MetadataAnnotation([this.resolutionState = STATE_NOT_STARTED]);
 
   MetadataAnnotation ensureResolved(Compiler compiler) {
     if (resolutionState == STATE_NOT_STARTED) {
       compiler.resolver.resolveMetadataAnnotation(this);
     }
     return this;
   }
 
   String toString() => 'MetadataAnnotation($value, $resolutionState)';
 }