Move resolveAlignment logic to RenderStyle

This CL moves resolveAlignment logic to RenderStyle as this seems
more appropriate place for this code. Also, the same logic is being
duplicated in both RenderGrid and RenderFlexible box, so it also
gets rid of duplicated code.

Review URL: https://codereview.chromium.org/547673002

git-svn-id: svn://svn.chromium.org/blink/trunk@183039 bbb929c8-8fbe-4397-9dbb-9b2b20218538