get assert if construct Directory with non-string

[DartBot]

This issue was originally filed by mattsh@google.com

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If you erroneously pass an int (rather than String) to a Directory object, you hit an assert in the vm.

for example:
    Directory dir = new Directory(25);
    dir.list();

You hit this assert:

dart_bin: ../runtime/bin/directory.cc:27: void Builtin_Directory_List(void*): Assertion `Dart_IsString(path)' failed.

[iposva-google]

Removed the owner.
Removed Area-Library label.
Added Area-IO, Triaged labels.

[madsager]

Set owner to @madsager.
Added Accepted label.

[madsager]

Which version of the standalone dart binary are you using? The dart binary has not been called dart_bin for quite some time.

I get an 'Illegal argument' exception when running the script above on tip of tree standalone Dart VM binary.

./out/Debug_ia32/dart dir.dart
Unhandled exception:
Illegal argument(s):
 0. Function: '_Directory@14117cc4._reportError@14117cc4' url: 'dart:io' line:861 col:7
 1. Function: '_Directory@14117cc4.function' url: 'dart:io' line:813 col:25
 2. Function: '_ReceivePortImpl@6be832b._handleMessage@6be832b' url: 'dart:isolate' line:288 col:22

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Added CannotReproduce label.

[kevmoo]

Removed Area-IO label.
Added Area-Library, Library-IO labels.