Update pubs detection of Isolate spawn errors, as the exception text was slightly changed.

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

 // Copyright (c) 2013, 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 pub.transformer_isolate;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:isolate';
 
@@ skipping 65 matching lines @@
           .then((_) => port.first)
           .then((sendPort) {
         return new TransformerIsolate._(sendPort, environment.mode, idsToUrls);
       }).catchError((error, stackTrace) {
         if (error is! CrossIsolateException) throw error;
         if (error.type != 'IsolateSpawnException') throw error;
 
         // TODO(nweiz): don't parse this as a string once issues 12617 and 12689
         // are fixed.
         var firstErrorLine = error.message.split('\n')[1];
-        var missingTransformer = idsToUrls.keys.firstWhere((id) =>
-                firstErrorLine.startsWith("Failure getting ${idsToUrls[id]}:"),
+        var missingTransformer = idsToUrls.keys.firstWhere(
+            (id) => firstErrorLine.startsWith(
+                "Uncaught Error: Failure getting ${idsToUrls[id]}:"),
             orElse: () => throw error);
         var packageUri = idToPackageUri(idsToAssetIds[missingTransformer]);
 
         // If there was an IsolateSpawnException and the import that actually
         // failed was the one we were loading transformers from, throw an
         // application exception with a more user-friendly message.
         fail('Transformer library "$packageUri" not found.',
             error, stackTrace);
       });
     });
@@ skipping 26 matching lines @@
 /// An error thrown when a transformer fails to load.
 class TransformerLoadError extends SourceSpanException
     implements WrappedException {
   final CrossIsolateException innerError;
   Chain get innerChain => innerError.stackTrace;
 
   TransformerLoadError(CrossIsolateException error, SourceSpan span)
       : innerError = error,
         super("Error loading transformer: ${error.message}", span);
 }