This makes it explicit when the --ignition-filter pattern should be
applied to the script name instead of the function name by using a
proper "s:{name}" pattern. It also hardcodes it to be a prefix match
instead of an exact match, because that is all we need for test262.

R=rmcilroy@chromium.org

Review URL: https://codereview.chromium.org/1389353002

Cr-Commit-Position: refs/heads/master@{#31153}