streams: add DataStream::GetMemoryUsage

src/streams.cpp

@@ -2,6 +2,7 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or https://opensource.org/license/mit/.
 
+#include <memusage.h>
 #include <span.h>
 #include <streams.h>
 #include <util/fs_helpers.h>
@@ -110,3 +111,8 @@ bool AutoFile::Truncate(unsigned size)
 {
     return ::TruncateFile(m_file, size);
 }
+
+size_t DataStream::GetMemoryUsage() const noexcept
+{
+    return sizeof(*this) + memusage::DynamicUsage(vch);
+}