We have a variety of ways that we link to specific places in the diff viewer, and one of the most common and useful is clicking on the link from a comment to jump straight to the comment in context. This was broken a while back. The fundamental cause here is that the `selectAnchor()` method is checking whether the comment flag's element is shown, but `TextBasedCommentBlock` defers its own show operation in order to let layout settle. We therefore were always bailing early. This change makes two fixes: - We now defer the whole operation for the `#startAtAnchorName` thing. This lets it run after comment flags have shown themselves. - We check the return value of `selectAnchor()` and verify that we actually did something before clearing out the saved anchor name. Testing Done: - Ran js-tests - Clicked on a bunch of links from diff comments and saw that they now properly scrolled the page. - Checked explicitly that a link to a comment on the last file on the page worked.