Add parent RenderStyle as argument to StyleResolver::styleForKeyframe()

When applying animation properties on an element during style resolve
the case where a default parent RenderStyle is provided was not handled
when building keyframe animations. This results in a crash when
attempting to resolve the use of inherit in a keyframe animation on the
body element during Document::inheritHtmlAndBodyElementStyles().

This patch ensures the correct parent RenderStyle is used in
StyleResolver::styleForKeyframe().

BUG=328997

Review URL: https://codereview.chromium.org/117093002

git-svn-id: svn://svn.chromium.org/blink/trunk@164037 bbb929c8-8fbe-4397-9dbb-9b2b20218538