Block webpages from navigating to view-source URLs.

This CL blocks navigations to view-source URLs initiated by a page via window.location, window.open, A tag, etc. It still allows user initiated navigations such as directly entering the URL, clicking "view page source" or "open in new tab" in the context menu.

BUG=247151,606619

Review-Url: https://codereview.chromium.org/1917073002
Cr-Commit-Position: refs/heads/master@{#397505}
10 files changed