Add chain support to barback.

sdk/lib/_internal/pub/lib/src/dart.dart

Index: sdk/lib/_internal/pub/lib/src/dart.dart
diff --git a/sdk/lib/_internal/pub/lib/src/dart.dart b/sdk/lib/_internal/pub/lib/src/dart.dart
index 7c5e0fa913142f9c33fa6bd320010b9f8fd539bd..2a5f938b5d4fca4b717e22cd84ccbdd6fd146a47 100644
--- a/sdk/lib/_internal/pub/lib/src/dart.dart
+++ b/sdk/lib/_internal/pub/lib/src/dart.dart
@@ -150,8 +150,8 @@ class CrossIsolateException implements Exception {
   /// property.
   final String message;
 
-  /// The exception's stack trace, or `null` if no stack trace was available.
-  final Trace stackTrace;
+  /// The exception's stack chain, or `null` if no stack chain was available.
+  final Chain stackTrace;
 
   /// Loads a [CrossIsolateException] from a serialized representation.
   ///
@@ -160,7 +160,7 @@ class CrossIsolateException implements Exception {
     var type = error['type'];
     var message = error['message'];
     var stackTrace = error['stack'] == null ? null :
-            new Trace.parse(error['stack']);
+            new Chain.parse(error['stack']);
     return new CrossIsolateException._(type, message, stackTrace);
   }
 
@@ -176,7 +176,7 @@ class CrossIsolateException implements Exception {
     return {
       'type': error.runtimeType.toString(),
       'message': getErrorMessage(error),
-      'stack': stack == null ? null : stack.toString()
+      'stack': stack == null ? null : new Chain.forTrace(stack).toString()
     };
   }