Add member localHostname() to the Dart IO Platform class.

runtime/bin/platform.h

Index: runtime/bin/platform.h
diff --git a/runtime/bin/platform.h b/runtime/bin/platform.h
index 8298b530d09ba0e96892b35c6548f5012a6bb64b..a3c44b6046d013a0d9d2e0b14487f01e794f03e1 100644
--- a/runtime/bin/platform.h
+++ b/runtime/bin/platform.h
@@ -24,6 +24,9 @@ class Platform {
   // string must be deallocated by the caller.
   static char* StrError(int error_code);
 
+  // Extracts the local hostname.
+  static bool LocalHostname(char *buffer, intptr_t buffer_length);
+
  private:
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(Platform);