Only inherit the animation mode when inheriting CSSPropertyTransitionProperty

Currently, when inheriting transition and animation properties, we always
inherit the animation mode also. This means that if the element from which
we're inheriting has a different animation mode, it will affect the computed
value of our CSSPropertyTransitionProperty property.

This is incorrect. We only need to inherit the animation mode when inheriting
the CSSPropertyTransitionProperty property itself.

Adds a new test to cover this and cleans up existing
related tests.

R=dstockwell

Review URL: https://codereview.chromium.org/79543005

git-svn-id: svn://svn.chromium.org/blink/trunk@162475 bbb929c8-8fbe-4397-9dbb-9b2b20218538