Apply outline-offset on all edges (not just top/left)

Apply outline-offset on all edges (not just top/left)

In InlinePainter::paintOutlineForLine, the "outline rectangles" are
formed by expanding and shifting by outline-offset. This however only
result in an offset of the outline on the top and left sides.
Rewrite the code to use an inflate() operation instead, so that all
four edges are affected by the offset.
The spec describes the effect of the 'outline-offset' property as:

  "If the computed value of outline-offset is anything other than 0,
   then the outline is outset from the border edge by that amount."
  "Negative values must cause the outline to shrink into the border
   box."

(http://dev.w3.org/csswg/css-ui-3/#outline-offset)

This is also what ObjectPainter::paintOutline does.

This makes us match Gecko more closely rendering-wise.

TEST=fast/inline/outline-offset.html (S.P. strict cull rect)
BUG=495368
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=197589

[fs, 2015-06-22 12:43:31]

fs@opera.com changed reviewers:
+ chrishtr@chromium.org, fmalita@chromium.org

[fs, 2015-06-22 13:32:26]

Not a whole lot of test-coverage for this, so I added a simple rendering test.
Sample outout:

https://storage.googleapis.com/chromium-layout-test-archives/linux_blink_rel/...

Looks pretty horrid (but did so prior to this fix too) for the outline-offset !=
0 cases, but hopefully that will be fixed/improved upon with crbug.com/502531.

[chrishtr, 2015-06-22 18:19:40]

The CQ bit was checked by chrishtr@chromium.org

[chrishtr, 2015-06-22 18:19:41]

lgtm

[commit-bot: I haz the power, 2015-06-22 18:20:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1201753003/1

[commit-bot: I haz the power, 2015-06-22 18:24:44]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=197589