Reuse thread when writing stdout/stderr on Windows.

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 87a0b30e2f5350a91da3cfdd841f0967243d14ce..a5d55a9fff5c39717e2f5ce14e92fd3cfabbbdeb 100644
--- a/runtime/bin/socket_win.cc
+++ b/runtime/bin/socket_win.cc
@@ -198,11 +198,11 @@ intptr_t Socket::GetStdioHandle(intptr_t num) {
   if (handle == INVALID_HANDLE_VALUE) {
     return -1;
   }
-  FileHandle* file_handle = new FileHandle(handle);
-  if (file_handle == NULL) return -1;
-  file_handle->MarkDoesNotSupportOverlappedIO();
-  file_handle->EnsureInitialized(EventHandler::delegate());
-  return reinterpret_cast<intptr_t>(file_handle);
+  StdHandle* std_handle = new StdHandle(handle);
+  if (std_handle == NULL) return -1;
+  std_handle->MarkDoesNotSupportOverlappedIO();
+  std_handle->EnsureInitialized(EventHandler::delegate());
+  return reinterpret_cast<intptr_t>(std_handle);
 }