Keep only base/extractor.[cc|h].

third_party/lzma/v4_65/files/CPP/7zip/Common/OffsetStream.cpp

-// OffsetStream.cpp
-
-#include "StdAfx.h"
-
-#include "Common/Defs.h"
-#include "OffsetStream.h"
-
-HRESULT COffsetOutStream::Init(IOutStream *stream, UInt64 offset)
-{
-  _offset = offset;
-  _stream = stream;
-  return _stream->Seek(offset, STREAM_SEEK_SET, NULL);
-}
-
-STDMETHODIMP COffsetOutStream::Write(const void *data, UInt32 size, UInt32 *processedSize)
-{
-  return _stream->Write(data, size, processedSize);
-}
-
-STDMETHODIMP COffsetOutStream::Seek(Int64 offset, UInt32 seekOrigin,
-    UInt64 *newPosition)
-{
-  UInt64 absoluteNewPosition;
-  if (seekOrigin == STREAM_SEEK_SET)
-    offset += _offset;
-  HRESULT result = _stream->Seek(offset, seekOrigin, &absoluteNewPosition);
-  if (newPosition != NULL)
-    *newPosition = absoluteNewPosition - _offset;
-  return result;
-}
-
-STDMETHODIMP COffsetOutStream::SetSize(Int64 newSize)
-{
-  return _stream->SetSize(_offset + newSize);
-}