Can more conveniently set easing from JS.

chrome/browser/resources/vr_shell/vr_shell_ui_api.js

Index: chrome/browser/resources/vr_shell/vr_shell_ui_api.js
diff --git a/chrome/browser/resources/vr_shell/vr_shell_ui_api.js b/chrome/browser/resources/vr_shell/vr_shell_ui_api.js
index 4bbb4830b5fba55947d6a859c79fb71feb8ade7b..7bb04d619e16bce5b926769dba596f96dd16a3f5 100644
--- a/chrome/browser/resources/vr_shell/vr_shell_ui_api.js
+++ b/chrome/browser/resources/vr_shell/vr_shell_ui_api.js
@@ -333,7 +333,7 @@ api.Property = {
  * @enum {number}
  * @const
  */
-api.Easing = {
+api.EasingType = {
   'LINEAR': 0,
   'CUBICBEZIER': 1,
   'EASEIN': 2,
@@ -341,6 +341,46 @@ api.Easing = {
 };
 
 /**
+ * Abstract easing base class.
+ * @abstract

[cjgrant, 2017/02/16 14:51:47]

Nice!  I missed that @abstract exists.  Could you apply it to
NativeCommandHandler as well?

[tiborg, 2017/02/16 17:30:49]

Done. Also added to fill class.

+ */
+api.Easing = class {
+  constructor(type) {
+    this.type = type;
+  }
+}
+
+api.LinearEasing = class extends api.Easing {
+  constructor() {
+    super(api.EasingType.LINEAR);
+  }
+}
+
+api.CubicBezierEasing = class extends api.Easing {
+  constructor(p1x, p1y, p2x, p2y) {

[mthiesse, 2017/02/16 15:12:06]

We should provide reasonable defaults for all easing parameters. Josh originally
pushed back on even having them as part of the API and wanted us to just provide
good values natively. At least if there are defaults here he can tweak them.

[tiborg, 2017/02/16 17:30:49]

Makes sense. Done.

+    super(api.EasingType.CUBICBEZIER);
+    this.p1x = p1x;
+    this.p1y = p1y;
+    this.p2x = p2x;
+    this.p2y = p2y;
+  }
+}
+
+api.InEasing = class extends api.Easing {
+  constructor(pow) {
+    super(api.EasingType.EASEIN);
+    this.pow = pow;
+  }
+}
+
+api.OutEasing = class extends api.Easing {
+  constructor(pow) {
+    super(api.EasingType.EASEOUT);
+    this.pow = pow;
+  }
+}
+
+/**
  * Base animation class. An animation can vary only one object property.
  * @struct
  */
@@ -355,7 +395,7 @@ api.Animation = class {
     /** @private {Object} */
     this.to = {};
     /** @private {Object} */
-    this.easing = {};
+    this.easing = new api.LinearEasing();
 
     // How many milliseconds in the future to start the animation.
     /** @private {number} */
@@ -364,8 +404,6 @@ api.Animation = class {
     // Duration of the animation (milliseconds).
     /** @private {number} */
     this.durationMillis = durationMs;
-
-    this.easing.type = api.Easing.LINEAR;
   }
 
   /**
@@ -436,6 +474,14 @@ api.Animation = class {
     this.property = api.Property.OPACITY;
     this.to.x = opacity;
   }
+
+  /**
+   * Set the animation's easing.
+   * @param {api.Easing} easing
+   */
+  setEasing(easing) {
+    this.easing = easing;
+  }
 };
 
 /**