Make root-zone handleUncaughtError rethrow with the correct stack.

runtime/lib/errors.cc

 // 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.
 
 #include "vm/bootstrap_natives.h"
 #include "vm/exceptions.h"
 #include "vm/object_store.h"
 #include "vm/runtime_entry.h"
 #include "vm/stack_frame.h"
 
@@ skipping 108 matching lines @@
   args.SetAt(1, String::Handle(script.url()));
   intptr_t line;
   script.GetTokenLocation(error_pos, &line, NULL);
   args.SetAt(2, Smi::Handle(Smi::New(line)));
 
   Exceptions::ThrowByType(Exceptions::kAbstractClassInstantiation, args);
   UNREACHABLE();
   return Object::null();
 }
 
+// Rethrow an error with a stacktrace.
+DEFINE_NATIVE_ENTRY(Zone_rethrow, 2) {
+  GET_NON_NULL_NATIVE_ARGUMENT(Instance, error, arguments->NativeArgAt(0));
+  GET_NON_NULL_NATIVE_ARGUMENT(Instance, stacktrace, arguments->NativeArgAt(1));
+  Exceptions::ReThrow(thread, error, stacktrace);
+  return Object::null();
+}
+
 }  // namespace dart