Fix presubmit check output when the items are AffectedFile instances.

R=dpranke@chromium.org
BUG=none
TEST=none

Review URL: http://codereview.chromium.org/6676093

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@79217 0039d316-1c4b-4281-b951-d872f2087c98

presubmit_support.py

@@ -146,7 +146,7 @@ class OutputApi(object):
       for index, item in enumerate(self._items):
         output.write('  ')
         # Write separately in case it's unicode.
-        output.write(item)
+        output.write(str(item))
         if index < len(self._items) - 1:
           output.write(' \\')
         output.write('\n')