[ios] Fix ChromeBrowserStateClient to report a correct value

ChromeBrowserStateClient returned a hardcoded value of "1" when asked
for the number of BrowserStates as using browser_state_info_cache.h
would have introduced a circular dependency.

Fix the circular dependency by moving browser_state_info_cache.h from
the //ios/chrome/browser/browser_state:browser_state_impl target to
the //ios/chrome/browser/browser_state target instead.

Bug: 991575
Change-Id: I589fa36db8dc0e85d546982aaa096fd5a958b23d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2521001


Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Mike Pinkerton <pinkerton@chromium.org>
Auto-Submit: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824843}