[TexMap] Use visible as initial value of backface-visibility-property.
https://bugs.webkit.org/show_bug.cgi?id=108875

Patch by JungJik Lee <jungjik.lee@samsung.com> on 2013-02-05
Reviewed by Noam Rosenthal.

According to W3C spec, the initial value of backface-visibility-visibility is visible.
However TextureMapperLayer's initial value is false which means hidden.
So this patch is for changing the value to visible(true).

Covered by existing tests.

* platform/graphics/texmap/TextureMapperLayer.h:
(WebCore::TextureMapperLayer::State::State): Change the initial value false to true
to use backface-visibility.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@141885 268f45cc-cd09-0410-ab3c-d52691b4dbfc