Many websites use simple calls to String.prototype.indexOf with either a
one character ASCII needle or needles bigger than the search string. This
CL adds a TFJ builtin for these simple cases, giving up to factor 5 speedup.

Drive-by-fix: Add default Object type to Arguments.at

BUG=

Review-Url: https://codereview.chromium.org/2539093002
Cr-Commit-Position: refs/heads/master@{#41760}