Gardening: inspector/debugger/debugger-script-preprocessor.html is flaky.

BUG=310924
TBR=antonm@chromium.org

Review URL: https://codereview.chromium.org/39113002

git-svn-id: svn://svn.chromium.org/blink/trunk@160404 bbb929c8-8fbe-4397-9dbb-9b2b20218538