Add MultiSourceInformationStrategy

tests/compiler/dart2js/sourcemaps/js_tracer.dart

 // Copyright (c) 2016, 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 sourcemap.js_tracer;
 
 import 'package:compiler/src/io/source_information.dart';
 import 'package:compiler/src/io/position_information.dart';
 import 'package:compiler/src/js/js.dart' as js;
+import 'package:compiler/src/js/js_source_mapping.dart';
 import 'sourcemap_helper.dart';
 import 'trace_graph.dart';
 
 /// Create a [TraceGraph] for [info] registering usage in [coverage].
 TraceGraph createTraceGraph(SourceMapInfo info, Coverage coverage) {
   TraceGraph graph = new TraceGraph();
   TraceListener listener = new StepTraceListener(graph);
   CodePositionMap codePositions =
       new CodePositionCoverage(info.jsCodePositions, coverage);
   JavaScriptTracer tracer = new JavaScriptTracer(
-      codePositions, [new CoverageListener(coverage), listener]);
+      codePositions, const SourceInformationReader(), [
+    new CoverageListener(coverage, const SourceInformationReader()),
+    listener
+  ]);
   info.node.accept(tracer);
   return graph;
 }
 
 class StepTraceListener extends TraceListener
     with NodeToSourceInformationMixin {
   Map<js.Node, TraceStep> steppableMap = <js.Node, TraceStep>{};
   final TraceGraph graph;
 
   StepTraceListener(this.graph);
 
+  SourceInformationReader get reader => const SourceInformationReader();
+
   @override
   void onStep(js.Node node, Offset offset, StepKind kind) {
     SourceInformation sourceInformation = computeSourceInformation(node);
     SourcePositionKind sourcePositionKind = SourcePositionKind.START;
     List text = [node];
     switch (kind) {
       case StepKind.FUN_ENTRY:
         text = ['<entry>'];
         break;
       case StepKind.FUN_EXIT:
@@ skipping 84 matching lines @@
         branch = '$value';
         break;
     }
     graph.pushBranch(branch);
   }
 
   void popBranch() {
     graph.popBranch();
   }
 }