Web Animations: Fix error in clock update logic and re-enable timeline-time test

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 3faae36ec8297090a7c285fa5f9ed8c245a23b71..6afcc6f8e089954cf5e96a6842312ae8e7c289fc 100644
--- a/Source/core/animation/AnimationClock.cpp
+++ b/Source/core/animation/AnimationClock.cpp
@@ -64,6 +64,8 @@ double AnimationClock::currentTime()
             ASSERT(newTime >= currentTime);
             ASSERT(newTime <= currentTime + approximateFrameTime);
             updateTime(newTime);
+        } else {
+            m_currentTask = s_currentTask;
         }
     }
     return m_time;