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I think that this patch is a good starting point for outline implementation.
It implements a basic outline painting algorithm:
- Outlines are painted by containing self painting fragment.
- Outlines are computed as:
   traverse fragment's descendants
   combine outlines for fragments with common layout objects
   paint combined outlines, using first fragment as DisplayItem

There are many problems:
- All descendant fragments are traversed for each outline paint, even if
  there are no outlines to be painted.
  Fix: detect outline existence while descendants are being painted,
  and only call this code if there are outlines.

There are 119 tests in our test suite that trigger inline outline paint code.
With this patch, we get 4 regressions:
fast/history/visited-link-hover-outline-color.html
paint/invalidation/overflow/inline-block-overflow-repaint.html
paint/invalidation/overflow/inline-box-overflow-repaint.html
  cause: improper invalidation
fast/inline/nested-text-descendants.html
  cause: inline text position

15 additional tests pass.

Bug: 714962
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_layout_ng;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: Icccd225abac7e38fd9a871ee2914ff8d235474e3
Reviewed-on: https://chromium-review.googlesource.com/887633
Commit-Queue: Aleks Totic <atotic@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532270}