Switch Linux Auru ports over to POSIX SHM instead of legacy SYSV SHM.

ppapi/proxy/serialized_structs.h

 // 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_PROXY_SERIALIZED_STRUCTS_H_
 #define PPAPI_PROXY_SERIALIZED_STRUCTS_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 101 matching lines @@
 };
 
 struct PPPDecryptor_Buffer {
   ppapi::HostResource resource;
   uint32_t size;
   base::SharedMemoryHandle handle;
 };
 
 #if defined(OS_WIN)
 typedef HANDLE ImageHandle;
-#elif defined(OS_MACOSX) || defined(OS_ANDROID)
+#elif defined(TOOLKIT_GTK)
+// On legacy X Windows this is a SysV shared memory key.
+typedef int ImageHandle;
+#else
 typedef base::SharedMemoryHandle ImageHandle;
-#else
-// On X Windows this is a SysV shared memory key.
-typedef int ImageHandle;
 #endif
 
 }  // namespace proxy
 }  // namespace ppapi
 
 #endif  // PPAPI_PROXY_SERIALIZED_STRUCTS_H_