Fix Animations, Remove Compostior Animations.

This patch (re)hooks up animations so they start and removes the infrastructure required by blink to synchronize the compositor and main threads.

R=ojan@chromium.org

Review URL: https://codereview.chromium.org/772673002

examples/animation/basic.sky

+<sky>
+
+<div id="test">
+Hello, Sky
+</div>
+<script>
+window.addEventListener('load', function() {
+  var div = document.getElementById('test');
+  div.animate([
+    { backgroundColor: 'red', opacity: 1 },
+    { backgroundColor: 'green', opacity: 0}],
+    {
+      duration: 1000,
+      iterations: 2
+    });
+});
+</script>
+</sky>