dart2js cleanup: remove unused imports and variables

pkg/compiler/lib/src/io/position_information.dart

 // Copyright (c) 2015, 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.
 
 /// Source information system mapping that attempts a semantic mapping between
 /// offsets of JavaScript code points to offsets of Dart code points.
 
 library dart2js.source_information.position;
 
 import '../common.dart';
-import '../elements/elements.dart' show AstElement, FieldElement, LocalElement;
+import '../elements/elements.dart' show AstElement, FieldElement;
 import '../js/js.dart' as js;
+import '../js/js_debug.dart';
 import '../js/js_source_mapping.dart';
-import '../js/js_debug.dart';
 import '../tree/tree.dart' show FunctionExpression, Node, Send;
-
 import 'code_output.dart' show CodeBuffer;
 import 'source_file.dart';
 import 'source_information.dart';
 
 /// [SourceInformation] that consists of an offset position into the source
 /// code.
 class PositionSourceInformation extends SourceInformation {
   @override
   final SourceLocation startPosition;
 
@@ skipping 1254 matching lines @@
 
   @override
   CodePosition operator [](js.Node node) {
     CodePosition codePosition = codePositions[node];
     if (codePosition == null) {
       coverage.registerNodesWithoutOffset(node);
     }
     return codePosition;
   }
 }