Fix test flake in animation-state-changes-positive-playback-rate.html

The flake is caused by limited precision of timeline times. When
comparing times with >=, the boundary time needs to factor in error
tolerance.

The virtual/threaded-no-composited-antialiasing variant of this test
had a recent flake score of 954.

Bug: 623434
Change-Id: I44b41da1326849da4b3dec30cea76be6673e0b17
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2368500Reviewed-by: Xida Chen <xidachen@chromium.org>
Commit-Queue: Kevin Ellis <kevers@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801013}

third_party/blink/web_tests/animations/web-animations/animation-state-changes-positive-playback-rate.html

@@ -417,8 +417,10 @@ async_test(function(t) {
   var timelineCurrentTime = document.timeline.currentTime;
   animation.ready.then(t.step_func_done(() => {
     assert_equals(animation.playState, 'running');
-    assert_greater_than_equal(animation.startTime, timelineCurrentTime);
-    assert_greater_than_equal(animation.currentTime, animationCurrentTime);
+    assert_time_greater_than_equal(animation.startTime,
+                                   timelineCurrentTime);
+    assert_time_greater_than_equal(animation.currentTime,
+                                   animationCurrentTime);
   }));
 }, "PlayState is 'running' while playing a cancelled animation");
 
@@ -429,7 +431,8 @@ async_test(function(t) {
   animation.ready.then(t.step_func_done(() => {
     assert_equals(animation.playState, 'paused');
     assert_equals(animation.startTime, null);
-    assert_greater_than_equal(animation.currentTime, animationCurrentTime);
+    assert_time_greater_than_equal(animation.currentTime,
+                                   animationCurrentTime);
   }));
 }, "PlayState is 'running' while pausing a running animation");
 </script>

third_party/blink/web_tests/external/wpt/web-animations/testcommon.js

@@ -25,6 +25,15 @@ if (!window.assert_times_equal) {
   };
 }
 
+// Allow implementations to substitute an alternative method for comparing
+// times based on their precision requirements.
+if (!window.assert_time_greater_than_equal) {
+ window.assert_time_greater_than_equal = (actual, expected, description) => {
+    assert_greater_than_equal(actual, expected - 2 * TIME_PRECISION,
+                              description);
+  };
+}
+
 // Allow implementations to substitute an alternative method for comparing
 // a time value based on its precision requirements with a fixed value.
 if (!window.assert_time_equals_literal) {
@@ -305,4 +314,4 @@ function assert_phase_at_time(animation, phase, currentTime) {
                       + ` is ${currentTime}ms`
                       + ' (progress is non-null with appropriate fill mode)');
   }
-}
\ No newline at end of file
+}