Fix keyTimes list length of from/to/by animations.

For from/to/by animations, the length of keyTimes and keyPoints
attribute if are specified must be equal and must have at least
2 values.

R=fs@opera.com,dschulze@chromium.org
BUG=377050

Review URL: https://codereview.chromium.org/453243003

git-svn-id: svn://svn.chromium.org/blink/trunk@180390 bbb929c8-8fbe-4397-9dbb-9b2b20218538