Mojo: DataPipe: Implement "may discard" mode for simple writes.

mojo/system/data_pipe.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 "mojo/system/data_pipe.h"
 
 #include <string.h>
 
 #include <algorithm>
 #include <limits>
@@ skipping 19 matching lines @@
   };
   if (!in_options) {
     *out_options = kDefaultOptions;
     return MOJO_RESULT_OK;
   }
 
   if (in_options->struct_size < sizeof(*in_options))
     return MOJO_RESULT_INVALID_ARGUMENT;
   out_options->struct_size = static_cast<uint32_t>(sizeof(*out_options));
 
+  // All flags are okay (unrecognized flags will be ignored).
+  out_options->flags = in_options->flags;
+
   if (in_options->element_num_bytes == 0)
     return MOJO_RESULT_INVALID_ARGUMENT;
   out_options->element_num_bytes = in_options->element_num_bytes;
 
   if (in_options->capacity_num_bytes == 0) {
     // Round the default capacity down to a multiple of the element size (but at
     // least one element).
     out_options->capacity_num_bytes = std::max(
         static_cast<uint32_t>(kDefaultDataPipeCapacityBytes -
             (kDefaultDataPipeCapacityBytes % in_options->element_num_bytes)),
@@ skipping 258 matching lines @@
 void DataPipe::AwakeConsumerWaitersForStateChangeNoLock() {
   lock_.AssertAcquired();
   if (!has_local_consumer_no_lock())
     return;
   consumer_waiter_list_->AwakeWaitersForStateChange(
       ConsumerSatisfiedFlagsNoLock(), ConsumerSatisfiableFlagsNoLock());
 }
 
 }  // namespace system
 }  // namespace mojo