Implement frame state and animation architecture

src/ol/easing.js

@@ -0,0 +1,14 @@
+goog.provide('ol.easing');
+
+
+/**
+ * @param {number} t Input between 0 and 1.
+ * @return {number} Output between 0 and 1.
+ */
+ol.easing.upAndDown = function(t) {
+  if (t < 0.5) {
+    return goog.fx.easing.inAndOut(2 * t);
+  } else {
+    return 1 - goog.fx.easing.inAndOut(2 * (t - 0.5));
+  }
+};