Seaming on border corners with mixed colour alpha borders

Seaming on border corners with mixed colour alpha borders
https://bugs.webkit.org/show_bug.cgi?id=70471

Patch by Ben Wells <benwells@chromium.org> on 2011-11-16
Reviewed by Simon Fraser.

Source/WebCore:

Seaming is fixed by antialiasing mitred corners for edges that have alpha and are joining
a side that is of a different color.

Test: fast/borders/border-mixed-alpha.html

* rendering/RenderBoxModelObject.cpp:
(WebCore::colorNeedsAntiAliasAtCorner):
(WebCore::RenderBoxModelObject::paintOneBorderSide):

LayoutTests:

* fast/borders/border-mixed-alpha.html: Added.
* platform/chromium/test_expectations.txt:
* platform/mac/fast/borders/border-mixed-alpha-expected.png: Added.
* platform/mac/fast/borders/border-mixed-alpha-expected.txt: Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@100528 268f45cc-cd09-0410-ab3c-d52691b4dbfc