Revert of Revert of Make SharedMemoryHandle a class on Mac.

ppapi/proxy/nacl_message_scanner.cc

 // Copyright 2013 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 "ppapi/proxy/nacl_message_scanner.h"
 
 #include <vector>
 #include "base/bind.h"
 #include "ipc/ipc_message.h"
 #include "ipc/ipc_message_macros.h"
@@ skipping 275 matching lines @@
       it != file_systems_.end(); ++it)
     delete it->second;
   for (FileIOMap::iterator it = files_.begin(); it != files_.end(); ++it)
     delete it->second;
 }
 
 // Windows IPC differs from POSIX in that native handles are serialized in the
 // message body, rather than passed in a separate FileDescriptorSet. Therefore,
 // on Windows, any message containing handles must be rewritten in the POSIX
 // format before we can send it to the NaCl plugin.
+// On Mac, base::SharedMemoryHandle has a different serialization than
+// base::FileDescriptor (which base::SharedMemoryHandle is typedef-ed to in
+// OS_NACL).
 bool NaClMessageScanner::ScanMessage(
     const IPC::Message& msg,
     uint32_t type,
     std::vector<SerializedHandle>* handles,
     scoped_ptr<IPC::Message>* new_msg_ptr) {
   DCHECK(handles);
   DCHECK(handles->empty());
   DCHECK(new_msg_ptr);
   DCHECK(!new_msg_ptr->get());
 
   bool rewrite_msg =
-#if defined(OS_WIN)
+#if defined(OS_WIN) || defined(OS_MACOSX)
       true;
 #else
       false;
 #endif
 
   // We can't always tell from the message ID if rewriting is needed. Therefore,
   // scan any message types that might contain a handle. If we later determine
   // that there are no handles, we can cancel the rewriting by clearing the
   // results.new_msg pointer.
   ScanningResults results;
@@ skipping 197 matching lines @@
             fio_it->second->SetMaxWrittenOffset(offset_it->second);
         }
       }
       break;
     }
   }
 }
 
 }  // namespace proxy
 }  // namespace ppapi