Add NullWriteBuffer

dbms/src/IO/NullWriteBuffer.cpp

+#include <IO/NullWriteBuffer.h>
+
+
+namespace DB
+{
+
+NullWriteBuffer::NullWriteBuffer(size_t buf_size, char * existing_memory, size_t alignment)
+    : BufferWithOwnMemory<WriteBuffer>(buf_size, existing_memory, alignment)
+{
+}
+
+void NullWriteBuffer::nextImpl()
+{
+}
+
+}

dbms/src/IO/NullWriteBuffer.h

+#pragma once
+
+#include <IO/WriteBuffer.h>
+#include <IO/BufferWithOwnMemory.h>
+#include <boost/noncopyable.hpp>
+
+namespace DB
+{
+
+/// Simply do nothing, can be used to measure amount of written bytes.
+class NullWriteBuffer : public BufferWithOwnMemory<WriteBuffer>, boost::noncopyable
+{
+public:
+    NullWriteBuffer(size_t buf_size = 16<<10, char * existing_memory = nullptr, size_t alignment = false);
+    void nextImpl() override;
+};
+
+}