HostResolver is exposed to plugin.

ppapi/thunk/ppb_host_resolver_private_api.h

Index: ppapi/thunk/ppb_host_resolver_private_api.h
diff --git a/ppapi/thunk/ppb_host_resolver_private_api.h b/ppapi/thunk/ppb_host_resolver_private_api.h
new file mode 100644
index 0000000000000000000000000000000000000000..3067d5653fd01415262dfd9865941d189d76e7f9
--- /dev/null
+++ b/ppapi/thunk/ppb_host_resolver_private_api.h
@@ -0,0 +1,31 @@
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef PPAPI_THUNK_PPB_HOST_RESOLVER_PRIVATE_API_H_
+#define PPAPI_THUNK_PPB_HOST_RESOLVER_PRIVATE_API_H_
+
+#include "ppapi/c/private/ppb_host_resolver_private.h"
+#include "ppapi/thunk/ppapi_thunk_export.h"
+
+namespace ppapi {
+namespace thunk {
+
+class PPAPI_THUNK_EXPORT PPB_HostResolver_Private_API {
+ public:
+  virtual ~PPB_HostResolver_Private_API() {}
+
+  virtual int32_t Resolve(const char* host,
+                          uint16_t port,
+                          const PP_HostResolver_Private_Hint* hint,
+                          PP_CompletionCallback callback) = 0;
+  virtual uint32_t GetSize() = 0;
+  virtual bool GetItem(uint32_t index,
+                       PP_Var* canonname,
+                       PP_NetAddress_Private* addr) = 0;
+};
+
+}  // namespace thunk
+}  // namespace ppapi
+
+#endif  // PPAPI_THUNK_PPB_TCP_SOCKET_PRIVATE_API_H_