fix(animations): ensure a null easing value is never used with web-animations

Closes #9780
Closes #9752

modules/@angular/platform-browser/src/dom/web_animations_driver.ts

@@ -48,13 +48,18 @@ export class WebAnimationsDriver implements AnimationDriver {
       formattedSteps = [start, start];
     }
 
-    var playerOptions = {
+    var playerOptions: {[key: string]: string | number} = {
       'duration': duration,
       'delay': delay,
-      'easing': easing,
       'fill': 'both'  // we use `both` because it allows for styling at 0% to work with `delay`
     };
 
+    // we check for this to avoid having a null|undefined value be present
+    // for the easing (which results in an error for certain browsers #9752)
+    if (easing) {
+      playerOptions['easing'] = easing;
+    }
+
     var player = this._triggerWebAnimation(anyElm, formattedSteps, playerOptions);
 
     return new WebAnimationsPlayer(player, duration);

modules/@angular/platform-browser/test/dom/web_animations_driver_spec.ts

@@ -12,6 +12,7 @@ import {el} from '@angular/platform-browser/testing/browser_util';
 import {AnimationKeyframe, AnimationStyles} from '../../core_private';
 import {DomAnimatePlayer} from '../../src/dom/dom_animate_player';
 import {WebAnimationsDriver} from '../../src/dom/web_animations_driver';
+import {StringMapWrapper} from '../../src/facade/collection';
 import {MockDomAnimatePlayer} from '../../testing/mock_dom_animate_player';
 
 class ExtendedWebAnimationsDriver extends WebAnimationsDriver {
@@ -102,5 +103,16 @@ export function main() {
       var options = details['options'];
       expect(options['easing']).toEqual('ease-out');
     });
+
+    it('should only apply the provided easing if present', () => {
+      var startingStyles = _makeStyles({});
+      var styles = [_makeKeyframe(0, {'color': 'green'}), _makeKeyframe(1, {'color': 'red'})];
+
+      driver.animate(elm, startingStyles, styles, 1000, 1000, null);
+      var details = driver.log.pop();
+      var options = details['options'];
+      var keys = StringMapWrapper.keys(options);
+      expect(keys.indexOf('easing')).toEqual(-1);
+    });
   });
 }