dart2js: remove trailing 0 byte when reading .packages

pkg/compiler/lib/src/apiimpl.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.
 
 library leg_apiimpl;
 
 import 'dart:async';
 import 'dart:convert';
 
 import 'package:package_config/packages.dart';
@@ skipping 374 matching lines @@
   Future setupPackages(Uri uri) {
     if (packageRoot != null) {
       // Use "non-file" packages because the file version requires a [Directory]
       // and we can't depend on 'dart:io' classes.
       packages = new NonFilePackagesDirectoryPackages(packageRoot);
     } else if (packageConfig != null) {
       return callUserProvider(packageConfig).then((packageConfigContents) {
         if (packageConfigContents is String) {
           packageConfigContents = UTF8.encode(packageConfigContents);
         }
+        // The input provider may put a trailing 0 byte when it reads a source
+        // file, which confuses the package config parser.
+        if (packageConfigContents.length > 0
+            && packageConfigContents.last == 0) {
+          packageConfigContents = packageConfigContents.sublist(
+              0, packageConfigContents.length - 1);
+        }
         packages =
             new MapPackages(pkgs.parse(packageConfigContents, packageConfig));
       });
     } else {
       if (packagesDiscoveryProvider == null) {
         packages = Packages.noPackages;
       } else {
         return callUserPackagesDiscovery(uri).then((p) {
           packages = p;
         });
@@ skipping 86 matching lines @@
     print('$message: ${tryToString(exception)}');
     print(tryToString(stackTrace));
   }
 
   fromEnvironment(String name) => environment[name];
 
   LibraryInfo lookupLibraryInfo(String libraryName) {
     return library_info.LIBRARIES[libraryName];
   }
 }