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

mojo/system/data_pipe_consumer_dispatcher.cc

Index: mojo/system/data_pipe_consumer_dispatcher.cc
diff --git a/mojo/system/data_pipe_consumer_dispatcher.cc b/mojo/system/data_pipe_consumer_dispatcher.cc
index b4fb423e54fc88e170279adf8389ad3aa0b537e9..4f459fcc70ba27f24c15f77487139b32777a97d2 100644
--- a/mojo/system/data_pipe_consumer_dispatcher.cc
+++ b/mojo/system/data_pipe_consumer_dispatcher.cc
@@ -51,33 +51,28 @@ DataPipeConsumerDispatcher::CreateEquivalentDispatcherAndCloseImplNoLock() {
 }
 
 MojoResult DataPipeConsumerDispatcher::ReadDataImplNoLock(
-    void* elements,
-    uint32_t* num_bytes,
+    UserPointer<void> elements,
+    UserPointer<uint32_t> num_bytes,
     MojoReadDataFlags flags) {
   lock().AssertAcquired();
 
-  if (!VerifyUserPointer<uint32_t>(num_bytes))
-    return MOJO_RESULT_INVALID_ARGUMENT;
-
   if ((flags & MOJO_READ_DATA_FLAG_DISCARD)) {
     // These flags are mutally exclusive.
     if ((flags & MOJO_READ_DATA_FLAG_QUERY))
       return MOJO_RESULT_INVALID_ARGUMENT;
-    DVLOG_IF(2, elements) << "Discard mode: ignoring non-null |elements|";
+    DVLOG_IF(2, !elements.IsNull())
+        << "Discard mode: ignoring non-null |elements|";
     return data_pipe_->ConsumerDiscardData(
         num_bytes, (flags & MOJO_READ_DATA_FLAG_ALL_OR_NONE));
   }
 
   if ((flags & MOJO_READ_DATA_FLAG_QUERY)) {
     DCHECK(!(flags & MOJO_READ_DATA_FLAG_DISCARD));  // Handled above.
-    DVLOG_IF(2, elements) << "Query mode: ignoring non-null |elements|";
+    DVLOG_IF(2, !elements.IsNull())
+        << "Query mode: ignoring non-null |elements|";
     return data_pipe_->ConsumerQueryData(num_bytes);
   }
 
-  // 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));
 }