- Label as "bigint" in DevTools heap snapshot viewer
- Treat as new primitive in injected-script-source
- Show primitive value as property for BigIntObject
- Adds the "n" suffix onto description, both with/without inspector
  being present

Bug: v8:7486
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng;master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I47a02e32f9bdd9124a6c91056965574ecd443867
Reviewed-on: https://chromium-review.googlesource.com/940804
Commit-Queue: Erik Luo <luoe@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51855}