Base JavaScript code position computation on JavaScript tracer.

tests/compiler/dart2js/sourcemaps/trace_graph.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.
+
+library sourcemap.trace_graph;
+
+import 'dart:collection';
+
+import 'package:compiler/src/io/source_information.dart';
+import 'package:compiler/src/io/position_information.dart';
+
+import 'sourcemap_html_helper.dart';
+
+class TraceGraph {
+  List<TraceStep> steps = <TraceStep>[];
+  TraceStep entry;
+  Queue stack = new Queue();
+
+  void addStep(TraceStep step) {
+    steps.add(step);
+    step.stack = stack.toList();
+  }
+
+  void pushBranch(branch) {
+    stack.addLast(branch);
+  }
+
+  void popBranch() {
+    stack.removeLast();
+  }
+}
+
+class TraceStep<N> {

[Siggi Cherem (dart-lang), 2016/01/21 18:18:35]

drop the generic? Make it directly use js.Node below? Or add the generic in
TraceGraph and in js_tracer?

[Johnni Winther, 2016/01/22 15:12:39]

Removed for now.

+  final int id;
+  final N node;
+  final Offset offset;
+  final List text;
+  final SourceLocation sourceLocation;
+
+  TraceStep next;
+  Map<dynamic, TraceStep> branchMap;
+
+  List stack;
+
+  TraceStep(
+      this.id,
+      this.node,
+      this.offset,
+      this.text,
+      [this.sourceLocation]);
+
+  String toString() => '<span style="background:${toColorCss(id)}">$id</span>';
+}
+