Copy the (early prototype of) remoting in Chrome into the public tree....

remoting/host/differ_block.h

+// Copyright (c) 2010 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 REMOTING_HOST_DIFFER_BLOCK_H_
+#define REMOTING_HOST_DIFFER_BLOCK_H_
+
+#include "base/basictypes.h"
+
+namespace remoting {
+
+// Low level functions to return the difference between 2 blocks of pixels.
+// The amount of difference is returned as an int.
+//   zero means the blocks are identical.
+//   larger values indicate larger changes.
+// Pixel format of the captured screen may be platform specific, but constant.
+// Size of block is constant.
+
+int BlockDifference(const uint8* image1, const uint8* image2, int stride);
+
+}  // namespace remoting
+
+#endif  // REMOTING_HOST_DIFFER_BLOCK_H_