Merge sdch/open-vcdiff from http://git.chromium.org/external/open-vcdiff.git at 438f2a5be6d809bc21611a94cd37bfc8c28ceb33

This commit was generated by merge-from-chromium.py.

Change-Id: I10bf1f306f3f7d57cef2a7a4a67a22a35fa7b188