Add Dart code to diff_view

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 '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]);
   info.node.accept(tracer);
   return graph;
 }
 
-class StepTraceListener extends TraceListener {
+class StepTraceListener extends TraceListener
+    with NodeToSourceInformationMixin {
   Map<js.Node, TraceStep> steppableMap = <js.Node, TraceStep>{};
   final TraceGraph graph;
 
   StepTraceListener(this.graph);
 
   @override
   void onStep(js.Node node, Offset offset, StepKind kind) {
-    SourceInformation sourceInformation = node.sourceInformation;
+    SourceInformation sourceInformation = computeSourceInformation(node);
     SourcePositionKind sourcePositionKind = SourcePositionKind.START;
     List text = [node];
     switch (kind) {
       case StepKind.FUN:
         sourcePositionKind = SourcePositionKind.INNER;
         text = ['<exit>'];
         break;
       case StepKind.CALL:
         CallPosition callPosition =
             CallPosition.getSemanticPositionForCall(node);
@@ skipping 30 matching lines @@
         js.Do doNode = node;
         text = ['do {... } (', doNode.condition, ')'];
         break;
       case StepKind.SWITCH_EXPRESSION:
         js.Switch switchNode = node;
         text = ['switch(', switchNode.key, ') ...'];
         break;
 
     }
     createTraceStep(
+        kind,
         node,
         offset: offset,
         sourceLocation: getSourceLocation(
-            node.sourceInformation, sourcePositionKind),
+            sourceInformation, sourcePositionKind),
         text: text);
   }
 
   void createTraceStep(
+      StepKind kind,
       js.Node node,
       {Offset offset,
        List text,
        String note,
        SourceLocation sourceLocation}) {
     int id = steppableMap.length;
 
     if (text == null) {
       text = [node];
     }
 
     TraceStep step = new TraceStep(
-        id, node,
+        kind,
+        id,
+        node,
         offset,
-        text, sourceLocation);
+        text,
+        sourceLocation);
     graph.addStep(step);
 
     steppableMap[node] = step;
   }
 
 
   void pushBranch(BranchKind kind, [value]) {
     var branch;
     switch (kind) {
       case BranchKind.CONDITION:
@@ skipping 12 matching lines @@
         branch = '$value';
         break;
     }
     graph.pushBranch(branch);
   }
 
   void popBranch() {
     graph.popBranch();
   }
 }