Add the ability to change the working directory

runtime/bin/dartutils.cc

Index: runtime/bin/dartutils.cc
diff --git a/runtime/bin/dartutils.cc b/runtime/bin/dartutils.cc
index 3379b168ffde450f56e81d021b2dc8ee873ba2ac..a803fca4e4deee78074326eb7962123d808c39d1 100644
--- a/runtime/bin/dartutils.cc
+++ b/runtime/bin/dartutils.cc
@@ -566,9 +566,13 @@ Dart_Handle DartUtils::NewDartExceptionWithMessage(const char* library_url,
                                                    const char* message) {
   // Create a Dart Exception object with a message.
   Dart_Handle clazz = GetDartClass(library_url, exception_name);
-  Dart_Handle args[1];
-  args[0] = NewString(message);
-  return Dart_New(clazz, Dart_Null(), 1, args);
+  if (message != NULL) {
+    Dart_Handle args[1];
+    args[0] = NewString(message);
+    return Dart_New(clazz, Dart_Null(), 1, args);
+  } else {
+    return Dart_New(clazz, Dart_Null(), 0, NULL);
+  }
 }