Write an update in run-webkit-tests before looking for crash logs.

Symbolizing crash stacks may take quite a while, so we should write
an update to the logger indicating that that's what we're doing.

R=jochen@chromium.org, eseidel@chromium.org
BUG=323875

Review URL: https://codereview.chromium.org/102953005

git-svn-id: svn://svn.chromium.org/blink/trunk@163575 bbb929c8-8fbe-4397-9dbb-9b2b20218538