Support read-only duplicates of Mojo shared buffers.

mojo/edk/system/broker_posix.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 "mojo/edk/system/broker.h"
 
 #include <fcntl.h>
 #include <unistd.h>
 
 #include <utility>
@@ skipping 94 matching lines @@
              out_message->data_num_bytes()) {
     LOG(ERROR) << "Error sending complete broker message";
     return nullptr;
   }
 
   std::deque<PlatformHandle> incoming_platform_handles;
   if (WaitForBrokerMessage(sync_channel_.get(),
                            BrokerMessageType::BUFFER_RESPONSE, 1,
                            &incoming_platform_handles)) {
     return PlatformSharedBuffer::CreateFromPlatformHandle(
-        num_bytes, ScopedPlatformHandle(incoming_platform_handles.front()));
+        num_bytes, false /* read_only */,
+        ScopedPlatformHandle(incoming_platform_handles.front()));
   }
 
   return nullptr;
 }
 
 }  // namespace edk
 }  // namespace mojo