Create OWNERS file for ios/web_view/internal/sync.

jzw@ wrote most of this code and ichikawa@ reviewed most of the changes.
This CL effectively removes eugenebut@, michaeldo@ or rohitrao@ from
ios/web_view/internal/sync OWNERS, because these engineers are not very
familiar with the code.

Bug: None
Change-Id: I713d656aec887eee97969e3c7f6d29e100ea3f20
Reviewed-on: https://chromium-review.googlesource.com/c/1351416Reviewed-by: Hiroshi Ichikawa <ichikawa@chromium.org>
Commit-Queue: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611144}

ios/web_view/internal/sync/OWNERS

+ichikawa@chromium.org
+jzw@chromium.org
+
+# These are for the common case of adding or renaming files. If you're doing
+# structural changes, please get a review from an OWNER.
+per-file BUILD.gn=*
+
+# COMPONENT: Mobile>iOSWebView
+# TEAM: ios-directory-owners@chromium.org
+# OS: iOS