[CSS Grid Layout] Adapting align-self, align-items and justify-self to 
the last CSS 3 spec.

Added support and test cases for the new values, baseline last-baseline,
flex-start, flex-end. Properly set the initial value to 'auto' in all properties. 

Resolving the 'auto' Computed Value in the StyleAdjuster class, so it's
valid for both, CSSComputedStyleDeclaration and the corresponding
RenderObjects.

BUG=249451, 376823

Review URL: https://codereview.chromium.org/363133003

git-svn-id: svn://svn.chromium.org/blink/trunk@179307 bbb929c8-8fbe-4397-9dbb-9b2b20218538