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

mojo/system/core.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/core.h"
 
 #include <vector>
 
 #include "base/logging.h"
 #include "base/time/time.h"
@@ skipping 353 matching lines @@
 
 MojoResult Core::BeginWriteData(MojoHandle data_pipe_producer_handle,
                                 UserPointer<void*> buffer,
                                 UserPointer<uint32_t> buffer_num_bytes,
                                 MojoWriteDataFlags flags) {
   scoped_refptr<Dispatcher> dispatcher(
       GetDispatcher(data_pipe_producer_handle));
   if (!dispatcher)
     return MOJO_RESULT_INVALID_ARGUMENT;
 
-  return dispatcher->BeginWriteData(buffer.GetPointerUnsafe(),
-                                    buffer_num_bytes.GetPointerUnsafe(), flags);
+  return dispatcher->BeginWriteData(buffer, buffer_num_bytes, flags);
 }
 
 MojoResult Core::EndWriteData(MojoHandle data_pipe_producer_handle,
                               uint32_t num_bytes_written) {
   scoped_refptr<Dispatcher> dispatcher(
       GetDispatcher(data_pipe_producer_handle));
   if (!dispatcher)
     return MOJO_RESULT_INVALID_ARGUMENT;
 
   return dispatcher->EndWriteData(num_bytes_written);
@@ skipping 169 matching lines @@
   // |Wait()|/|WaitMany()| call. (Only after doing this can |waiter| be
   // destroyed, but this would still be required if the waiter were in TLS.)
   for (i = 0; i < num_added; i++)
     dispatchers[i]->RemoveWaiter(&waiter);
 
   return rv;
 }
 
 }  // namespace system
 }  // namespace mojo