The dotAll flag changes behavior of the dot '.' character to match every
possible single character instead of excluding certain line terminators.
The implementation is staged behind --harmony-regexp-dotall.
Spec proposal: https://github.com/mathiasbynens/es-regexp-dotall-flag
BUG=v8:6172
Review-Url: https://codereview.chromium.org/2780173002
Cr-Commit-Position: refs/heads/master@{#44295}