The i18n.js code was calling a lot of methods, which might have been
removed or replaced by user code.

Make sure we use the original functions.

BUG=v8:4220
LOG=N
R=adamk, littledan
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_chromium_rel_ng;tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1199813004

Cr-Commit-Position: refs/heads/master@{#29268}