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This is a new attempt at fixing bug 657157, previous attempts were
reverted due to regressions.

When setting accessibility focus to a node, auto-focus it if it's a link.
This is needed for some sites that have skip links that are only visible
when focused.

In addition, when following a same-page link, move accessibility focus
to the new target location on the page only after a short delay. This
avoids a race condition due to focus also changing at the same time.

Tested manually on three pages mentioned in bug 657157:
1. getbootstrap.com, which has a same-page link that's only visible
   when focused
2. http://jsfiddle.net/mev0c4dt/show/ - a test page for a regression
   that happened with a previous attempt to fix this bug
3. https://codepen.io/artesea/pen/jVdLXP - a test page for a regression
   that happened with a previous attempt to fix this bug

Bug: 657157
Change-Id: I791544af3074f5aac5116c6695332d8178da21d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1873964Reviewed-by: Akihiro Ota <akihiroota@chromium.org>
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710150}