https://bugs.webkit.org/show_bug.cgi?id=122837

Reviewed by Brent Fulgham.

Instead of stretching the vertical bar with the stretchable version, just repeat
the normal vertical bar. This follows what Gecko does when rendering tall vertical
bars and also works around an issue with STIX fonts leading to poor spacing in
formulas.

Source/WebCore:

* rendering/mathml/RenderMathMLOperator.cpp: Stretch the vertical bar with the
normal variant.

LayoutTests:

* mathml/presentation/mo-stretch.html: Reworked this test to show
stretching of all stretchable characters, which reveals a bug with
the double vertical bar (covered by http://wkbug.com/123543).
* platform/gtk/TestExpectations:
* platform/gtk/mathml/presentation/mo-stretch-expected.png:
* platform/gtk/mathml/presentation/mo-stretch-expected.txt:
* platform/mac/mathml/presentation/mo-stretch-expected.png:
* platform/mac/mathml/presentation/mo-stretch-expected.txt:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@158678 268f45cc-cd09-0410-ab3c-d52691b4dbfc