Removed BigInt and BigInt64Array, URLSearchParams#keys from
externs/pending.js since these have been added to the default compiler
externs.

Couple of notes:
 1) It is the first time a roll is fetching the closure compiler
    binary and externs from NPM.
 2) Any updates to chrome_extensions.js have been intentionally
    reverted from this CL, since they cause type-checking errors.
    Instead, a parallel effort is underway to stop using
    chrome_extensions.js in Chromium.

Bug: 1137293,1137350
Change-Id: I6a120b7a8e75aefa8a5dd3ce3c8d03fa33b3f745
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2464091
Commit-Queue: dpapad <dpapad@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#817064}