Mark inspector/jump-to-previous-editing-location.html as SLOW

This test is timing out on all platforms and there's no obvious cause.
This patch marks this test as SLOW for all platforms.

BUG=336481
NOTRY=true
TBR=eustas

Review URL: https://codereview.chromium.org/144223002

git-svn-id: svn://svn.chromium.org/blink/trunk@165484 bbb929c8-8fbe-4397-9dbb-9b2b20218538