[ios] Add thegreenfrog and michaeldo as owners of //ios/web/find_in_page.

Thegreenfrog has been responsible for creating all file contents in this
directory, landing 10+ CLs in the process.

Michaeldo has reviewed a majority of those CLs.

Bug: 919685
Change-Id: I4da69fbbeee987381c632a174528f1ce606a1b22
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1574461
Commit-Queue: Chris Lu <thegreenfrog@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652650}

ios/web/find_in_page/OWNERS

+michaeldo@chromium.org
+thegreenfrog@chromium.org
+
+# TEAM: ios-directory-owners@chromium.org
+# OS: iOS