Bug 1425771 - Tweak expected restyle count for the case where the animation begins at the current time. r=birtles

The expected restyle count depends both on animation state and micro task
handling.

If we have the conformant Promise handling and if the animation begins at the
current time, we will observe 1 less restyles than observed frames since we
skip the first restyle in the initial frame.  This represents correctly what
we do and what we *should* do.

If we don't have the conformant Promise handling and if the animation doesn't
begin at the current time, we will observe 1 more restyles than obsered frames
since the Promise in observeStyling (precisely the Promise is inside the
callback for requestAnimationFrame) is fulfilled once after a restyling process
followed by the requestAnimationFrame.

MozReview-Commit-ID: FLhSRx4y1V7

--HG--
extra : rebase_source : 59e2bb2439f69bc1415a441c0b84a81463d8229f

dom/animation/test/mozilla/file_restyles.html

@@ -99,6 +99,35 @@ function startsRightNow(aAnimation) {
          aAnimation.currentTime === 0;
 }
 
+function tweakExpectedRestyleCount(aAnimation, aExpectedRestyleCount) {
+  // Normally we expect one restyling for each requestAnimationFrame (as
+  // called by observeRestyling) PLUS one for the last frame becasue of bug
+  // 1193394.  However, we won't observe that initial restyling unless BOTH of
+  // the following two conditions hold:
+  //
+  // 1. We are running *before* restyling happens.
+  // 2. The animation actually needs a restyle because it started prior to
+  //    this frame.  Even if (1) is true, in some cases due to aligning with
+  //    the refresh driver, the animation fame in which the ready promise is
+  //    resolved happens to coincide perfectly with the start time of the
+  //    animation.  In this case no restyling is needed so we won't observe
+  //    an additional restyle.
+  if (hasConformantPromiseHandling) {
+    // If we have the conformant Promise handling and |aAnimation| begins at
+    // the current timeline time, we will not process restyling in the initial
+    // frame.
+    if (startsRightNow(aAnimation)) {
+      return aExpectedRestyleCount - 1;
+    }
+  } else if (!startsRightNow(aAnimation)) {
+    // If we don't have the conformant Promise handling and |aAnimation|
+    // doesn't begin at the current timeline time, we will see an additional
+    // restyling in the last frame.
+    return aExpectedRestyleCount + 1;
+  }
+  return aExpectedRestyleCount;
+}
+
 var omtaEnabled = isOMTAEnabled();
 
 var isAndroid = !!navigator.userAgent.includes("Android");
@@ -145,19 +174,9 @@ waitForAllPaints(() => {
     await animation.ready;
     ok(!SpecialPowers.wrap(animation).isRunningOnCompositor);
 
-    // Normally we expect one restyling for each requestAnimationFrame (as
-    // called by observeRestyling) PLUS one for the last frame becasue of bug
-    // 1193394.  However, we won't observe that initial restyling unless BOTH of
-    // the following two conditions hold:
-    //
-    // 1. We are running *before* restyling happens.
-    // 2. The animation actually needs a restyle because it started prior to
-    //    this frame.  Even if (1) is true, in some cases due to aligning with
-    //    the refresh driver, the animation fame in which the ready promise is
-    //    resolved happens to coincide perfectly with the start time of the
-    //    animation.  In this case no restyling is needed so we won't observe
-    //    an additional restyle.
-    const expectedRestyleCount = !startsRightNow(animation) ? 6 : 5;
+    // We need to tweak expected restyle count depending on animation state and
+    // micro task handling.
+    const expectedRestyleCount = tweakExpectedRestyleCount(animation, 5);
     var markers = await observeStyling(5);
     is(markers.length, expectedRestyleCount,
        'CSS animations running on the main-thread should update style ' +
@@ -1005,7 +1024,7 @@ waitForAllPaints(() => {
 
     await animation.ready;
 
-    const expectedRestyleCount = !startsRightNow(animation) ? 6 : 5;
+    const expectedRestyleCount = tweakExpectedRestyleCount(animation, 5);
     var markers = await observeStyling(5);
 
     is(markers.length, expectedRestyleCount,
@@ -1073,7 +1092,7 @@ waitForAllPaints(() => {
     var animation = rect.animate({ fill: ['blue', 'lime'] }, 100 * MS_PER_SEC);
     await animation.ready;
 
-    const expectedRestyleCount = !startsRightNow(animation) ? 6 : 5;
+    const expectedRestyleCount = tweakExpectedRestyleCount(animation, 5);
     var markers = await observeStyling(5);
     is(markers.length, expectedRestyleCount,
        'CSS animations on an in-view svg element with post-transform should ' +
@@ -1134,7 +1153,7 @@ waitForAllPaints(() => {
     var animation = targetDiv.getAnimations()[0];
     await animation.ready;
 
-    const expectedRestyleCount = !startsRightNow(animation) ? 6 : 5;
+    const expectedRestyleCount = tweakExpectedRestyleCount(animation, 5);
     var markers = await observeStyling(5);
     is(markers.length, expectedRestyleCount,
        'CSS animation on an in-view element with pre-transform should not ' +