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

mojo/system/data_pipe.h

 // 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.
 
 #ifndef MOJO_SYSTEM_DATA_PIPE_H_
 #define MOJO_SYSTEM_DATA_PIPE_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
@@ skipping 59 matching lines @@
   void ConsumerCancelAllWaiters();
   void ConsumerClose();
   // This does not validate its arguments, except to check that |*num_bytes| is
   // a multiple of |element_num_bytes_|.
   MojoResult ConsumerReadData(void* elements,
                               uint32_t* num_bytes,
                               bool all_or_none);
   MojoResult ConsumerDiscardData(uint32_t* num_bytes,
                                  bool all_or_none);
   MojoResult ConsumerQueryData(uint32_t* num_bytes);
-  // This does not validate its arguments.
-  MojoResult ConsumerBeginReadData(const void** buffer,
-                                   uint32_t* buffer_num_bytes,
+  MojoResult ConsumerBeginReadData(UserPointer<const void*> buffer,
+                                   UserPointer<uint32_t> buffer_num_bytes,
                                    bool all_or_none);
   MojoResult ConsumerEndReadData(uint32_t num_bytes_read);
   MojoResult ConsumerAddWaiter(Waiter* waiter,
                                MojoHandleSignals signals,
                                uint32_t context);
   void ConsumerRemoveWaiter(Waiter* waiter);
   bool ConsumerIsBusy() const;
 
  protected:
   DataPipe(bool has_local_producer,
@@ skipping 19 matching lines @@
 
   virtual void ConsumerCloseImplNoLock() = 0;
   // |*num_bytes| will be a nonzero multiple of |element_num_bytes_|.
   virtual MojoResult ConsumerReadDataImplNoLock(void* elements,
                                                 uint32_t* num_bytes,
                                                 bool all_or_none) = 0;
   virtual MojoResult ConsumerDiscardDataImplNoLock(uint32_t* num_bytes,
                                                    bool all_or_none) = 0;
   // |*num_bytes| will be a nonzero multiple of |element_num_bytes_|.
   virtual MojoResult ConsumerQueryDataImplNoLock(uint32_t* num_bytes) = 0;
-  virtual MojoResult ConsumerBeginReadDataImplNoLock(const void** buffer,
-                                                     uint32_t* buffer_num_bytes,
-                                                     bool all_or_none) = 0;
+  virtual MojoResult ConsumerBeginReadDataImplNoLock(
+      UserPointer<const void*> buffer,
+      UserPointer<uint32_t> buffer_num_bytes,
+      uint32_t min_num_bytes_to_read) = 0;
   virtual MojoResult ConsumerEndReadDataImplNoLock(uint32_t num_bytes_read) = 0;
   // Note: A consumer should not be writable during a two-phase read.
   virtual HandleSignalsState ConsumerGetHandleSignalsStateNoLock() const = 0;
 
   // Thread-safe and fast (they don't take the lock):
   bool may_discard() const { return may_discard_; }
   size_t element_num_bytes() const { return element_num_bytes_; }
   size_t capacity_num_bytes() const { return capacity_num_bytes_; }
 
   // Must be called under lock.
@@ skipping 61 matching lines @@
   uint32_t producer_two_phase_max_num_bytes_written_;
   uint32_t consumer_two_phase_max_num_bytes_read_;
 
   DISALLOW_COPY_AND_ASSIGN(DataPipe);
 };
 
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_SYSTEM_DATA_PIPE_H_