Use a pool of native ports for directory operations

runtime/bin/directory.h

Index: runtime/bin/directory.h
diff --git a/runtime/bin/directory.h b/runtime/bin/directory.h
index 16c8443f383099a5c875e3e86ac1482d94a17261..7a507cc661c07e5741d1056713f54cb61278aa24 100644
--- a/runtime/bin/directory.h
+++ b/runtime/bin/directory.h
@@ -8,6 +8,7 @@
 #include "bin/builtin.h"
 #include "bin/dartutils.h"
 #include "platform/globals.h"
+#include "platform/thread.h"
 
 class DirectoryListing {
  public:
@@ -63,6 +64,14 @@ class Directory {
 
   static bool Delete(const char* path, bool recursive);
 
+  static Dart_Port GetServicePort();
+
+ private:
+  static dart::Mutex mutex_;
+  static int service_ports_size_;
+  static Dart_Port* service_ports_;
+  static int service_ports_index_;
+
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(Directory);
 };