Refactor location computation in dart2js mirrors.

tests/compiler/dart2js/mirrors_test.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.
 
 import '../../../sdk/lib/_internal/compiler/implementation/mirrors/mirrors.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/mirrors/mirrors_util.dart';
 
 import 'dart:io';
 
 int count(Iterable iterable) {
@@ skipping 288 matching lines @@
   var metadata9 = metadata[9];
   Expect.isTrue(metadata9 is InstanceMirror);
   Expect.isFalse(metadata9.hasReflectee);
   Expect.throws(() => metadata9.reflectee, (_) => true);
   Expect.equals(metadataType.originalDeclaration, metadata9.type);
   metadata9.getField('data').then((InstanceMirror data) {
     Expect.isNotNull(data);
     Expect.isTrue(data.hasReflectee);
     Expect.isNull(data.reflectee);
   });
+
+  //////////////////////////////////////////////////////////////////////////////
+  // Location test
+  //////////////////////////////////////////////////////////////////////////////
+
+  var fooClassLocation = fooClass.location;
+  Expect.isNotNull(fooClassLocation);
+  // Expect the location to start with the first metadata.
+  Expect.equals(348, fooClassLocation.offset, "Unexpected offset");
+  // Expect the location to end with the class body.
+  Expect.equals(227, fooClassLocation.length, "Unexpected length");
+  Expect.equals(17, fooClassLocation.line, "Unexpected line");
+  Expect.equals(1, fooClassLocation.column, "Unexpected column");
+
 }
 
 // Testing abstract class Bar:
 //
 // abstract class Bar<E> {
 //
 // }
 void testBar(MirrorSystem system, LibraryMirror helperLibrary,
              Map<String,TypeMirror> classes) {
   var barClass = classes["Bar"];
@@ skipping 618 matching lines @@
   Expect.isTrue(privateFactoryConstructor.isPrivate);
   Expect.isFalse(privateFactoryConstructor.isConstConstructor);
   Expect.isFalse(privateFactoryConstructor.isRedirectingConstructor);
   Expect.isFalse(privateFactoryConstructor.isGenerativeConstructor);
   Expect.isTrue(privateFactoryConstructor.isFactoryConstructor);
 
   var metadata = privateClass.metadata;
   Expect.isNotNull(metadata);
   Expect.equals(0, metadata.length);
 }