Fix ppapi sample when built on windows.

native_client_sdk/src/examples/api/vpn_provider/vpn_provider.cc

 // Copyright 2016 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.
 
 #include <queue>
 #include <sstream>
 #include <string>
 
 #include "ppapi/cpp/instance.h"
 #include "ppapi/cpp/module.h"
 #include "ppapi/cpp/var.h"
 #include "ppapi/cpp/var_dictionary.h"
 
 #include "vpn_provider_helper.h"
 
+#ifdef WIN32
+# undef PostMessage
+#endif
+
 class VpnProviderInstance : public pp::Instance {
  public:
   explicit VpnProviderInstance(PP_Instance instance)
       : pp::Instance(instance), vpn_provider_helper_(this) {
     vpn_provider_helper_.Init();
   }
 
   virtual ~VpnProviderInstance() {}
 
   // Handles messages from Javascript
@@ skipping 102 matching lines @@
   }
 };
 
 namespace pp {
 
 Module* CreateModule() {
   return new VpnProviderModule();
 }
 
 }  // namespace pp