When a diff contains utf8 character, the filename would be stored as a unicode
object instead of a str. This is even if the buffer is originally sent as a
utf-8 encoded str. Then once the diff is reconstructed to be sent to 'patch', a
unicode object instead of a str would be sent, confusing patch.

R=cmp@chromium.org
BUG=
TEST=


Review URL: http://codereview.chromium.org/9387024

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@122361 0039d316-1c4b-4281-b951-d872f2087c98