Add patch for functional changes to unrar

This CL adds a patch file detailing the functional changes made to unrar
within the Chromium source.

Bug: 910302
Change-Id: I6546759ca482a0f3baa9f2166cb41d1214f1bf6b
Reviewed-on: https://chromium-review.googlesource.com/c/1357214
Reviewed-by: Varun Khaneja <vakh@chromium.org>
Commit-Queue: Daniel Rubery <drubery@chromium.org>
Cr-Commit-Position: refs/heads/master@{#613651}