Convert BeginReadData...() 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 394 matching lines @@
 
 MojoResult Core::BeginReadData(MojoHandle data_pipe_consumer_handle,
                                UserPointer<const void*> buffer,
                                UserPointer<uint32_t> buffer_num_bytes,
                                MojoReadDataFlags flags) {
   scoped_refptr<Dispatcher> dispatcher(
       GetDispatcher(data_pipe_consumer_handle));
   if (!dispatcher)
     return MOJO_RESULT_INVALID_ARGUMENT;
 
-  return dispatcher->BeginReadData(buffer.GetPointerUnsafe(),
-                                   buffer_num_bytes.GetPointerUnsafe(), flags);
+  return dispatcher->BeginReadData(buffer, buffer_num_bytes, flags);
 }
 
 MojoResult Core::EndReadData(MojoHandle data_pipe_consumer_handle,
                              uint32_t num_bytes_read) {
   scoped_refptr<Dispatcher> dispatcher(
       GetDispatcher(data_pipe_consumer_handle));
   if (!dispatcher)
     return MOJO_RESULT_INVALID_ARGUMENT;
 
   return dispatcher->EndReadData(num_bytes_read);
@@ skipping 135 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