When a file contains a single line of text, svn diff will generate an odd hunk
header. Modify the hunk parsing code to accept this format.

R=dpranke@chromium.org
BUG=
TEST=


Review URL: http://codereview.chromium.org/9147056

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@117143 0039d316-1c4b-4281-b951-d872f2087c98