Async Cookies: Add UseCounter for entire API surface.

For the purposes of the Origin Trial, it is preferable to have a single
feature use counter cover the whole API.

We also want to understand the usage of each API part, so this CL adds a
CookieStoreAPI UseCounter that is updated by every API entry point,
while maintaining per-method UseCounters. The event accessors
({ExtendableCookieChangeEvent, CookieChangeEvent}.{changed, deleted})
did lose their individual counters, because having them counted under 2
counters would require custom V8 bindings, and the complexity isn't woth
it.

Bug: 729800
Change-Id: Ica133c9213afa64805a90512c0f89cfda66281f0
Reviewed-on: https://chromium-review.googlesource.com/1144244
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576651}
5 files changed