[Payment Request] Measure usage of languageCode.

This patch adds a use counter for PaymentAddress.languageCode to
validate that it's rarely used and can be be removed. Latest discussions
in W3C have placed it at risk in the spec:
https://github.com/w3c/payment-request/pull/764

Firefox and Safari have removed languageCode from their implementations.

Bug: 877521
Change-Id: I9e137d768be87c6dbc8affd3db3c2d6260ada46b
Reviewed-on: https://chromium-review.googlesource.com/1188489
Commit-Queue: Rouslan Solomakhin <rouslan@chromium.org>
Reviewed-by: Rick Byers <rbyers@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589289}
3 files changed