Convert BeginWriteData...() to use the new user pointer handling (see r285350).

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 102 matching lines @@
     return MOJO_RESULT_OK;  // Nothing to do.
 
   HandleSignalsState old_consumer_state = ConsumerGetHandleSignalsStateNoLock();
   MojoResult rv = ProducerWriteDataImplNoLock(elements, num_bytes, all_or_none);
   HandleSignalsState new_consumer_state = ConsumerGetHandleSignalsStateNoLock();
   if (!new_consumer_state.equals(old_consumer_state))
     AwakeConsumerWaitersForStateChangeNoLock(new_consumer_state);
   return rv;
 }
 
-MojoResult DataPipe::ProducerBeginWriteData(void** buffer,
-                                            uint32_t* buffer_num_bytes,
-                                            bool all_or_none) {
+MojoResult DataPipe::ProducerBeginWriteData(
+    UserPointer<void*> buffer,
+    UserPointer<uint32_t> buffer_num_bytes,
+    bool all_or_none) {
   base::AutoLock locker(lock_);
   DCHECK(has_local_producer_no_lock());
 
   if (producer_in_two_phase_write_no_lock())
     return MOJO_RESULT_BUSY;
   if (!consumer_open_no_lock())
     return MOJO_RESULT_FAILED_PRECONDITION;
 
-  if (all_or_none && *buffer_num_bytes % element_num_bytes_ != 0)
-    return MOJO_RESULT_INVALID_ARGUMENT;
+  uint32_t min_num_bytes_to_write = 0;
+  if (all_or_none) {
+    min_num_bytes_to_write = buffer_num_bytes.Get();
+    if (min_num_bytes_to_write % element_num_bytes_ != 0)
+      return MOJO_RESULT_INVALID_ARGUMENT;
+  }
 
   MojoResult rv = ProducerBeginWriteDataImplNoLock(buffer, buffer_num_bytes,
-                                                   all_or_none);
+                                                   min_num_bytes_to_write);
   if (rv != MOJO_RESULT_OK)
     return rv;
   // Note: No need to awake producer waiters, even though we're going from
   // writable to non-writable (since you can't wait on non-writability).
   // Similarly, though this may have discarded data (in "may discard" mode),
   // making it non-readable, there's still no need to awake consumer waiters.
   DCHECK(producer_in_two_phase_write_no_lock());
   return MOJO_RESULT_OK;
 }
 
@@ skipping 245 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