Fix issue 13942 - Dart_Error function invokes OS::VSNPrint with the "format" string containing data…

runtime/bin/vmservice_impl.cc

Index: runtime/bin/vmservice_impl.cc
===================================================================
--- runtime/bin/vmservice_impl.cc	(revision 28804)
+++ runtime/bin/vmservice_impl.cc	(working copy)
@@ -290,10 +290,10 @@
                                          Dart_Handle library,
                                          Dart_Handle url) {
   if (!Dart_IsLibrary(library)) {
-    return Dart_Error("not a library");
+    return Dart_NewApiError("not a library");
   }
   if (!Dart_IsString(url)) {
-    return Dart_Error("url is not a string");
+    return Dart_NewApiError("url is not a string");
   }
   const char* url_string = NULL;
   Dart_Handle result = Dart_StringToCString(url, &url_string);