Move crw_web_view_content_view files to ios/web/common.

Old header is included by another repo, so the old header was left for
backward compatibility to include the header from the new location.

features.h was temporarily moved to a separate gn target to avoid
circular dependency. Later features.h will be moved to ios/web/common.

Bug: 942244
Change-Id: Ia362d277fca4abcaaa759d3bc29d382604d34163
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1531312
Commit-Queue: Eugene But <eugenebut@chromium.org>
Reviewed-by: Mike Dougherty <michaeldo@chromium.org>
Auto-Submit: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#642586}
12 files changed