Attempt to fix crashes in run-webkit-tests when running Android layout tests.

It looks like we may see cases where devices crash or go offline,
in which case the Android Port implementation attempts to run 'adb logcat'
to get more debugging information. I think when that command runs,
we get output back that isn't ASCII-safe and that is causing Python's
goofy str/unicode handling to get confused.

This patch attempts to protect against that. It is a mostly
hypothetical fix, as I haven't actually reproduced the fault locally.

TBR=peter@chromium.org
BUG=386343

Review URL: https://codereview.chromium.org/577133002

git-svn-id: svn://svn.chromium.org/blink/trunk@182214 bbb929c8-8fbe-4397-9dbb-9b2b20218538