Add unittest for ios/web/web_view/wk_web_view_util.

This CL adds an unittest containing one test case for
wk_web_view_util.IsSafeBrowsingWarningDisplayedInWebView. Notice that
private API of WKPreferences and WKWebView are used in this test case to
enable safe browsing and to display the warning. It's also only
supported by iOS 12.2+.

Bug: 956511
Change-Id: Ib39f7b3ba544bbc07d3b579ac6bf29c619e25f7f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1617483
Commit-Queue: Yi Su <mrsuyi@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661291}
3 files changed