Web Animations: Timeline should not advance during task execution

Source/core/animation/AnimationClock.cpp

Index: Source/core/animation/AnimationClock.cpp
diff --git a/Source/core/animation/AnimationClock.cpp b/Source/core/animation/AnimationClock.cpp
index 649220690e67a27adf18592ac5d9a46d000c9ff2..e25af24f8a1a339d54ebb20b70d5cd0aa1a6cebd 100644
--- a/Source/core/animation/AnimationClock.cpp
+++ b/Source/core/animation/AnimationClock.cpp
@@ -35,18 +35,18 @@ namespace WebCore {
 
 void AnimationClock::updateTime(double time)
 {
-    if (time > m_time)
+    if (time > m_time) {
         m_time = time;
-    m_frozen = true;
+        // Avoid a race where the animation start time received
+        // from the compositor may be earlier than the task time.
+        taskTime() = 0;
+    }
 }
 
 double AnimationClock::currentTime()
 {
-    if (!m_frozen) {
-        double newTime = m_monotonicallyIncreasingTime();
-        if (newTime >= m_time + minTimeBeforeUnsynchronizedAnimationClockTick)
-            m_time = newTime;
-    }
+    if (m_time < taskTime())
+        m_time = taskTime();
     return m_time;
 }