Dart: Better handle leak checks. close() is async.

mojo/dart/embedder/isolate_data.h

Index: mojo/dart/embedder/isolate_data.h
diff --git a/mojo/dart/embedder/isolate_data.h b/mojo/dart/embedder/isolate_data.h
index bd29fe1ab2b2fef266f55806abb1c5d76f4a454a..69fd093d7719fe1a1ae6f1977aaefa5e0d944bf0 100644
--- a/mojo/dart/embedder/isolate_data.h
+++ b/mojo/dart/embedder/isolate_data.h
@@ -5,8 +5,7 @@
 #ifndef MOJO_DART_EMBEDDER_ISOLATE_DATA_H_
 #define MOJO_DART_EMBEDDER_ISOLATE_DATA_H_
 
-#include <stdlib.h>
-#include <string.h>
+#include <set>
 
 #include "base/callback.h"
 #include "base/macros.h"
@@ -43,6 +42,7 @@ class IsolateData {
   std::string script;
   std::string script_uri;
   std::string package_root;
+  std::set<int64_t> unclosed_handles;
 
   DISALLOW_COPY_AND_ASSIGN(IsolateData);
 };