Subzero: Include commit count in revision string.

Subzero: Include commit count in revision string.

Instead of the version string being like this:
  Subzero_revision_efdf412032f7622a0663696896708d75b82e92f6
Make it more like this:
  Subzero_revision_1089_efdf412032f7622a0663696896708d75b82e92f6
I.e., provide both git hash and commit count.

That way, it's easier to compare revision strings and determine which one is newer.

BUG= none
R=eholk@chromium.org

Review URL: https://codereview.chromium.org/2251153002 .