Support read-only duplicates of Mojo shared buffers.

mojo/edk/system/data_pipe_producer_dispatcher.cc

Index: mojo/edk/system/data_pipe_producer_dispatcher.cc
diff --git a/mojo/edk/system/data_pipe_producer_dispatcher.cc b/mojo/edk/system/data_pipe_producer_dispatcher.cc
index d8d8abf1791c0e1abefa8292c7bd4feaecbf3814..d3b2530035889b2a5446edd1f33596d096dc6563 100644
--- a/mojo/edk/system/data_pipe_producer_dispatcher.cc
+++ b/mojo/edk/system/data_pipe_producer_dispatcher.cc
@@ -385,6 +385,7 @@ DataPipeProducerDispatcher::Deserialize(const void* data,
   scoped_refptr<PlatformSharedBuffer> ring_buffer =
       PlatformSharedBuffer::CreateFromPlatformHandle(
           state->options.capacity_num_bytes,
+          false /* read_only */,
           ScopedPlatformHandle(buffer_handle));
   if (!ring_buffer) {
     DLOG(ERROR) << "Failed to deserialize shared buffer handle.";