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

runtime/bin/platform_win.cc

Index: runtime/bin/platform_win.cc
diff --git a/runtime/bin/platform_win.cc b/runtime/bin/platform_win.cc
index e1f9ced1f427cbc1c7f782303cebaf8d1bc3eede..115cdf097e7632178343e4f3671fa42c676270f7 100644
--- a/runtime/bin/platform_win.cc
+++ b/runtime/bin/platform_win.cc
@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 #include "bin/platform.h"
+#include "bin/socket.h"
 
 
 bool Platform::Initialize() {
@@ -23,6 +24,17 @@ const char* Platform::OperatingSystem() {
 }
 
 
+bool Platform::LocalHostname(char *buffer, intptr_t buffer_length) {
+  static bool socketInitialized = false;
+  if (!socketInitialized) {
+    // Initialize Socket for gethostname.
+    if (!Socket::Initialize()) return false;
+    socketInitialized = true;
+  }
+  return gethostname(buffer, buffer_length) == 0;
+}
+
+
 char* Platform::StrError(int error_code) {
   static const int kBufferSize = 1024;
   char* error = static_cast<char*>(malloc(kBufferSize));