Don't crash when mapping stack chains.

lib/source_map_stack_trace.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 source_map_stack_trace;
 
 import 'package:path/path.dart' as p;
 import 'package:source_maps/source_maps.dart';
 import 'package:stack_trace/stack_trace.dart';
 
 /// Convert [stackTrace], a stack trace generated by dart2js-compiled
 /// JavaScript, to a native-looking stack trace using [sourceMap].
 ///
 /// [minified] indicates whether or not the dart2js code was minified. If it
 /// hasn't, this tries to clean up the stack frame member names.
 ///
 /// [packageRoot] is the URI (usually a `file:` URI) for the package root that
 /// was used by dart2js. It can be a [String] or a [Uri]. If it's passed, stack
 /// frames from packages will use `package:` URLs.
 ///
 /// [sdkRoot] is the URI (usually a `file:` URI) for the SDK containing dart2js.
 /// It can be a [String] or a [Uri]. If it's passed, stack frames from the SDK
 /// will have `dart:` URLs.
 StackTrace mapStackTrace(Mapping sourceMap, StackTrace stackTrace,
     {bool minified: false, packageRoot, sdkRoot}) {
   if (stackTrace is Chain) {
     return new Chain(stackTrace.traces.map((trace) {
-      return mapStackTrace(trace, sourceMap,
-          minified: minified, packageRoot: packageRoot, sdkRoot: sdkRoot);
+      return new Trace.from(mapStackTrace(sourceMap, trace,
+          minified: minified, packageRoot: packageRoot, sdkRoot: sdkRoot));
     }));
   }
 
   if (packageRoot != null && packageRoot is! String && packageRoot is! Uri) {
     throw new ArgumentError(
         'packageRoot must be a String or a Uri, was "$packageRoot".');
   }
 
   if (sdkRoot != null && sdkRoot is! String && sdkRoot is! Uri) {
     throw new ArgumentError(
@@ skipping 58 matching lines @@
       .replaceAll(new RegExp(r"[a-zA-Z_0-9]+\$"), "")
       // Get rid of the static method prefix. The class name also exists in the
       // invocation, so we're not getting rid of any information.
       .replaceAll(new RegExp(r"^[a-zA-Z_0-9]+.static."), "")
       // Convert underscores after identifiers to dots. This runs the risk of
       // incorrectly converting members that contain underscores, but those are
       // contrary to the style guide anyway.
       .replaceAllMapped(new RegExp(r"([a-zA-Z0-9]+)_"),
           (match) => match[1] + ".");
 }