Use mutex around getaddrinfo on windows, as it's not thread-safe.

runtime/bin/socket_win.cc

Index: runtime/bin/socket_win.cc
diff --git a/runtime/bin/socket_win.cc b/runtime/bin/socket_win.cc
index 77c51ef92bc6648ce4f53e2e5c077b8465ae28c3..da82b273b68ec6385beeb2252cec366a395d6706 100644
--- a/runtime/bin/socket_win.cc
+++ b/runtime/bin/socket_win.cc
@@ -12,6 +12,8 @@
 #include "bin/socket.h"
 #include "bin/utils.h"
 
+#include "vm/thread.h"
+
 
 namespace dart {
 namespace bin {
@@ -217,11 +219,15 @@ intptr_t ServerSocket::Accept(intptr_t fd) {
 }
 
 
+static Mutex* getaddrinfo_mutex = new Mutex();
 AddressList<SocketAddress>* Socket::LookupAddress(const char* host,
                                                   int type,
                                                   OSError** os_error) {
   Initialize();
 
+  // getaddrinfo is not thread-safe on Windows. Use a mutex to get around it.
+  MutexLocker locker(getaddrinfo_mutex);
+
   // Perform a name lookup for a host name.
   struct addrinfo hints;
   memset(&hints, 0, sizeof(hints));