Clean up webkitpy.layout_tests.servers.crash_service implementation.

Just a bit of code cleanup to go along w/ the other changes in this series.

R=scottmg@chromium.org
BUG=30536

Review URL: https://codereview.chromium.org/135933007

git-svn-id: svn://svn.chromium.org/blink/trunk@167138 bbb929c8-8fbe-4397-9dbb-9b2b20218538