Fix for issue 26555, do not inherit package root and package config from the parent isolate when do…

runtime/lib/isolate_patch.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.
 
 import "dart:collection" show HashMap;
 import "dart:_internal";
 
 patch class ReceivePort {
   /* patch */ factory ReceivePort() = _ReceivePortImpl;
 
@@ skipping 294 matching lines @@
 
   /* patch */ static Future<Isolate> spawn(
       void entryPoint(message), var message,
       {bool paused: false, bool errorsAreFatal,
        SendPort onExit, SendPort onError}) async {
     // `paused` isn't handled yet.
     RawReceivePort readyPort;
     try {
       // The VM will invoke [_startIsolate] with entryPoint as argument.
       readyPort = new RawReceivePort();
-      var packageRoot = null;
-      var packageConfig = null;
-      if (Isolate._packageSupported()) {
-        packageRoot = (await Isolate.packageRoot)?.toString();
-        packageConfig = (await Isolate.packageConfig)?.toString();
-      }
 
+      // We do not inherit the package root or package config settings
+      // from the parent isolate, instead we use the values that were
+      // set on the command line.
+      var packageRoot = VMLibraryHooks.packageRootString;
+      var packageConfig = VMLibraryHooks.packageConfigString;
       var script = VMLibraryHooks.platformScript;
       if (script == null) {
         // We do not have enough information to support spawning the new
         // isolate.
         throw new UnsupportedError("Isolate.spawn");
       }
       if (script.scheme == "package") {
         script = await Isolate.resolvePackageUri(script);
       }
 
@@ skipping 242 matching lines @@
     try {
       return Uri.parse(_getCurrentRootUriStr());
     } catch (e, s) {
       return null;
     }
   }
 
   static String _getCurrentRootUriStr()
       native "Isolate_getCurrentRootUriStr";
 }