[mojo] Add CreateSharedBuffer method to Broker.

mojo/edk/embedder/platform_channel_utils_posix.h

 // Copyright 2014 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 MOJO_EDK_EMBEDDER_PLATFORM_CHANNEL_UTILS_POSIX_H_
 #define MOJO_EDK_EMBEDDER_PLATFORM_CHANNEL_UTILS_POSIX_H_
 
 #include <stddef.h>
 #include <sys/types.h>  // For |ssize_t|.
 
@@ skipping 49 matching lines @@
                                                         PlatformHandle* handles,
                                                         size_t num_handles);
 
 // Wrapper around |recvmsg()|, which will extract any attached file descriptors
 // (in the control message) to |PlatformHandle|s (and append them to
 // |platform_handles|). (This also handles |EINTR|.)
 MOJO_SYSTEM_IMPL_EXPORT ssize_t
 PlatformChannelRecvmsg(PlatformHandle h,
                        void* buf,
                        size_t num_bytes,
-                       std::deque<PlatformHandle>* platform_handles);
+                       std::deque<PlatformHandle>* platform_handles,
+                       bool should_block = false);
 
 }  // namespace edk
 }  // namespace mojo
 
 #endif  // MOJO_EDK_EMBEDDER_PLATFORM_CHANNEL_UTILS_POSIX_H_