Bug 1524480 - Trigger transitions in test_missing-keyframe-on-compositor.html; r=hiro

test_missing-keyframe-on-compositor.html assumes that calling Element.animate()
will flush style and trigger transitions. However, in this patch series we will
make Element.animate() stop flushing style (and the spec will also mandate
this). Once we do that, the expected transitions will no longer fire and this
test will fail. This patch updates the test to explicitly trigger transitions
before calling Element.animate().

Differential Revision: https://phabricator.services.mozilla.com/D18915

--HG--
extra : moz-landing-system : lando

dom/animation/test/style/test_missing-keyframe-on-compositor.html

@@ -76,6 +76,8 @@ promise_test(t => {
     getComputedStyle(div).opacity;
 
     div.style.opacity = '0.5';
+    getComputedStyle(div).opacity;
+
     div.animate({ opacity: 1 }, 100 * MS_PER_SEC);
 
     return waitForPaintsFlushed();
@@ -134,6 +136,8 @@ promise_test(t => {
     getComputedStyle(div).opacity;
 
     div.style.opacity = '0.5';
+    getComputedStyle(div).opacity;
+
     div.animate([{ offset: 0, opacity: 1 }], 100 * MS_PER_SEC);
 
     return waitForPaintsFlushed();
@@ -274,6 +278,8 @@ promise_test(t => {
     getComputedStyle(div).transform;
 
     div.style.transform = 'translateX(200px)';
+    getComputedStyle(div).transform;
+
     div.animate({ transform: 'translateX(400px)' }, 100 * MS_PER_SEC);
 
     return waitForPaintsFlushed();
@@ -334,6 +340,8 @@ promise_test(t => {
     getComputedStyle(div).transform;
 
     div.style.transform = 'translateX(200px)';
+    getComputedStyle(div).transform;
+
     div.animate([{ offset: 0, transform: 'translateX(300px)' }],
                 100 * MS_PER_SEC);