Remove scanBuiltinLibraries.

tests/compiler/dart2js/analyze_only_test.dart

 // Copyright (c) 2012, 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.
 
 // Smoke test of the dart2js compiler API.
 library analyze_only;
 
 import "package:expect/expect.dart";
 import 'dart:async';
 import "package:async_helper/async_helper.dart";
@@ skipping 26 matching lines @@
   print('options: $options\n');
   asyncStart();
   Future<String> result =
       compile(new Uri(scheme: 'main'),
               new Uri(scheme: 'lib', path: '/'),
               new Uri(scheme: 'package', path: '/'),
               localProvider, localHandler, options);
   result.then((String code) {
     onValue(code, errors, warnings);
   }, onError: (e) {
-      throw 'Compilation failed';
+    throw 'Compilation failed: ${Error.safeToString(e)}';
   }).then(asyncSuccess);
 }
 
 main() {
   runCompiler(
     "",
     [],
     (String code, List errors, List warnings) {
       Expect.isNull(code);
       Expect.equals(1, errors.length, 'errors=$errors');
@@ skipping 99 matching lines @@
   // --analyze-signatures-only implies --analyze-only
   runCompiler(
     "",
     ['--analyze-signatures-only', '--analyze-all'],
     (String code, List errors, List warnings) {
       Expect.isNull(code);
       Expect.isTrue(errors.isEmpty);
       Expect.isTrue(warnings.isEmpty);
     });
 }