Add MultiSourceInformationStrategy

tests/compiler/dart2js/source_mapping_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 'dart:async';
 import 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/io/code_output.dart';
 import 'package:compiler/src/io/source_file.dart';
 import 'package:compiler/src/io/source_information.dart';
@@ skipping 21 matching lines @@
   for (int i = 0; i < codeWithMarkers.length; ++i) {
     if (codeWithMarkers[i] == '@') {
       expectedLocations.add(i - expectedLocations.length);
     }
   }
   String code = codeWithMarkers.replaceAll('@', '');
 
   SourceFile sourceFile = new StringSourceFile.fromName('<test script>', code);
   asyncTest(() => compileAll(sourceFile).then((CodeOutput output) {
         Set<int> locations = new Set<int>();
-        output
+        SourceLocations sourceLocations = output.sourceLocations.single;
+        sourceLocations
             .forEachSourceLocation((int offset, SourceLocation sourcePosition) {
           if (sourcePosition != null &&
               sourcePosition.sourceUri == sourceFile.uri) {
             locations.add(sourcePosition.offset);
           }
         });
 
         for (int i = 0; i < expectedLocations.length; ++i) {
           int expectedLocation = expectedLocations[i];
           if (!locations.contains(expectedLocation)) {
@@ skipping 60 matching lines @@
   testSourceMapLocations(FUNCTIONS_TEST);
   testSourceMapLocations(RETURN_TEST);
   testSourceMapLocations(NOT_TEST);
   testSourceMapLocations(UNARY_TEST);
   testSourceMapLocations(BINARY_TEST);
   testSourceMapLocations(SEND_TEST);
   testSourceMapLocations(SEND_SET_TEST);
   testSourceMapLocations(LOOP_TEST);
   testSourceMapLocations(INTERCEPTOR_TEST);
 }