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

mojo/system/core_test_base.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_test_base.h"
 
 #include <vector>
 
 #include "base/compiler_specific.h"
 #include "base/logging.h"
@@ skipping 80 matching lines @@
   virtual MojoResult WriteDataImplNoLock(
       const void* /*elements*/,
       uint32_t* /*num_bytes*/,
       MojoWriteDataFlags /*flags*/) OVERRIDE {
     info_->IncrementWriteDataCallCount();
     lock().AssertAcquired();
     return MOJO_RESULT_UNIMPLEMENTED;
   }
 
   virtual MojoResult BeginWriteDataImplNoLock(
-      void** /*buffer*/,
-      uint32_t* /*buffer_num_bytes*/,
+      UserPointer<void*> /*buffer*/,
+      UserPointer<uint32_t> /*buffer_num_bytes*/,
       MojoWriteDataFlags /*flags*/) OVERRIDE {
     info_->IncrementBeginWriteDataCallCount();
     lock().AssertAcquired();
     return MOJO_RESULT_UNIMPLEMENTED;
   }
 
   virtual MojoResult EndWriteDataImplNoLock(
       uint32_t /*num_bytes_written*/) OVERRIDE {
     info_->IncrementEndWriteDataCallCount();
     lock().AssertAcquired();
@@ skipping 235 matching lines @@
 }
 
 void CoreTestBase_MockHandleInfo::IncrementCancelAllWaitersCallCount() {
   base::AutoLock locker(lock_);
   cancel_all_waiters_call_count_++;
 }
 
 }  // namespace test
 }  // namespace system
 }  // namespace mojo