Implement a MOJO_READ_DATA_FLAG_PEEK flag for data pipes.

mojo/edk/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/edk/system/data_pipe.h"
 
 #include <string.h>
 
 #include <algorithm>
 #include <limits>
@@ skipping 242 matching lines @@
   DVLOG_IF(2, consumer_in_two_phase_read_no_lock())
       << "Consumer closed with active two-phase read";
   consumer_two_phase_max_num_bytes_read_ = 0;
   ConsumerCloseImplNoLock();
   AwakeProducerWaitersForStateChangeNoLock(
       ProducerGetHandleSignalsStateImplNoLock());
 }
 
 MojoResult DataPipe::ConsumerReadData(UserPointer<void> elements,
                                       UserPointer<uint32_t> num_bytes,
-                                      bool all_or_none) {
+                                      bool all_or_none,
+                                      bool peek) {
   base::AutoLock locker(lock_);
   DCHECK(has_local_consumer_no_lock());
 
   if (consumer_in_two_phase_read_no_lock())
     return MOJO_RESULT_BUSY;
 
   uint32_t max_num_bytes_to_read = num_bytes.Get();
   if (max_num_bytes_to_read % element_num_bytes_ != 0)
     return MOJO_RESULT_INVALID_ARGUMENT;
 
   if (max_num_bytes_to_read == 0)
     return MOJO_RESULT_OK;  // Nothing to do.
 
   uint32_t min_num_bytes_to_read = all_or_none ? max_num_bytes_to_read : 0;
 
   HandleSignalsState old_producer_state =
       ProducerGetHandleSignalsStateImplNoLock();
   MojoResult rv = ConsumerReadDataImplNoLock(
-      elements, num_bytes, max_num_bytes_to_read, min_num_bytes_to_read);
+      elements, num_bytes, max_num_bytes_to_read, min_num_bytes_to_read, peek);
   HandleSignalsState new_producer_state =
       ProducerGetHandleSignalsStateImplNoLock();
   if (!new_producer_state.equals(old_producer_state))
     AwakeProducerWaitersForStateChangeNoLock(new_producer_state);
   return rv;
 }
 
 MojoResult DataPipe::ConsumerDiscardData(UserPointer<uint32_t> num_bytes,
                                          bool all_or_none) {
   base::AutoLock locker(lock_);
@@ skipping 171 matching lines @@
 void DataPipe::AwakeConsumerWaitersForStateChangeNoLock(
     const HandleSignalsState& new_consumer_state) {
   lock_.AssertAcquired();
   if (!has_local_consumer_no_lock())
     return;
   consumer_waiter_list_->AwakeWaitersForStateChange(new_consumer_state);
 }
 
 }  // namespace system
 }  // namespace mojo