Move referrer_util.h to ios/web/common.

ios/web/common directory contains common code shared between //ios/web
and the rest of the layers (//components, //ios/chrome, //ios/web_view).
This directory does not contain the public API to create and manage web
contents (//ios/web/public is public API directory).

Bug: 942244
Change-Id: I249dbb2b0bbae69b58632dfd4b7c3175657773a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1549579
Commit-Queue: Eugene But <eugenebut@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Auto-Submit: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#647906}
18 files changed