Remove some confused callers of confusingAndOftenMisusedAttached

There's no reason to check confusingAndOftenMisusedAttached before calling
Document::prepareForDestruction.

R=esprehn
BUG=299011

Review URL: https://chromiumcodereview.appspot.com/24970002

git-svn-id: svn://svn.chromium.org/blink/trunk@158519 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Web Animations CSS: Handle border-spacing property

BUG=240653
R=dstockwell

Review URL: https://chromiumcodereview.appspot.com/25132005

git-svn-id: svn://svn.chromium.org/blink/trunk@158520 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Web Animations: Promote AnimatableValue type member from variable to virtual function

Simplifies subclassing of AnimatableValue.

BUG=257591

Review URL: https://chromiumcodereview.appspot.com/25092008

git-svn-id: svn://svn.chromium.org/blink/trunk@158521 bbb929c8-8fbe-4397-9dbb-9b2b20218538