Tweak fix in r182214 to try and fix android crashes again.

Turns out I used str.decode('ascii') when I really wanted
str.encode('ascii') ... Hopefully this one works better.

TBR=peter@chromium.org
BUG=386343

Review URL: https://codereview.chromium.org/561643003

git-svn-id: svn://svn.chromium.org/blink/trunk@182282 bbb929c8-8fbe-4397-9dbb-9b2b20218538