Fix handling of 'auto' for 'rx' and 'ry' on <ellipse>

Per the spec[1][2], when 'auto' is specified for 'rx' or 'ry' the used
value of said property will be the used value of the other property
('rx' for 'ry' and vice versa.)

[1] https://svgwg.org/svg2-draft/geometry.html#RX
[2] https://svgwg.org/svg2-draft/geometry.html#RY

Bug: 861585
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Iec0a9179527a5b0e99cc6a0ec671e5b6d92f828b
Reviewed-on: https://chromium-review.googlesource.com/1128885
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#573457}
4 files changed