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

mojo/system/data_pipe_consumer_dispatcher.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_consumer_dispatcher.h"
 
 #include "base/logging.h"
 #include "mojo/system/data_pipe.h"
 #include "mojo/system/memory.h"
 
@@ skipping 65 matching lines @@
 
   // Only verify |elements| if we're neither discarding nor querying.
   if (!VerifyUserPointerWithSize<1>(elements, *num_bytes))
     return MOJO_RESULT_INVALID_ARGUMENT;
 
   return data_pipe_->ConsumerReadData(
       elements, num_bytes, (flags & MOJO_READ_DATA_FLAG_ALL_OR_NONE));
 }
 
 MojoResult DataPipeConsumerDispatcher::BeginReadDataImplNoLock(
-    const void** buffer,
-    uint32_t* buffer_num_bytes,
+    UserPointer<const void*> buffer,
+    UserPointer<uint32_t> buffer_num_bytes,
     MojoReadDataFlags flags) {
   lock().AssertAcquired();
 
-  if (!VerifyUserPointerWithCount<const void*>(buffer, 1))
-    return MOJO_RESULT_INVALID_ARGUMENT;
-  if (!VerifyUserPointer<uint32_t>(buffer_num_bytes))
-    return MOJO_RESULT_INVALID_ARGUMENT;
   // These flags may not be used in two-phase mode.
   if ((flags & MOJO_READ_DATA_FLAG_DISCARD) ||
       (flags & MOJO_READ_DATA_FLAG_QUERY))
     return MOJO_RESULT_INVALID_ARGUMENT;
 
   return data_pipe_->ConsumerBeginReadData(
       buffer, buffer_num_bytes, (flags & MOJO_READ_DATA_FLAG_ALL_OR_NONE));
 }
 
 MojoResult DataPipeConsumerDispatcher::EndReadDataImplNoLock(
@@ skipping 16 matching lines @@
   data_pipe_->ConsumerRemoveWaiter(waiter);
 }
 
 bool DataPipeConsumerDispatcher::IsBusyNoLock() const {
   lock().AssertAcquired();
   return data_pipe_->ConsumerIsBusy();
 }
 
 }  // namespace system
 }  // namespace mojo