Web Animations: Add tests for player state transitions and fix discovered issues

Source/core/animation/AnimationPlayer.cpp

Index: Source/core/animation/AnimationPlayer.cpp
diff --git a/Source/core/animation/AnimationPlayer.cpp b/Source/core/animation/AnimationPlayer.cpp
index 6d4e287345dd835980d56907164d16d1f4faa32a..68fb4c3e711dcd877b1b0176bc4ea27703ee5f6f 100644
--- a/Source/core/animation/AnimationPlayer.cpp
+++ b/Source/core/animation/AnimationPlayer.cpp
@@ -305,7 +305,7 @@ void AnimationPlayer::setCurrentTime(double newCurrentTime)
 
 void AnimationPlayer::setStartTime(double startTime)
 {
-    if (m_paused) // FIXME: Should this throw an exception?
+    if (m_paused || m_idle)
         return;
     if (!std::isfinite(startTime))
         return;
@@ -458,18 +458,8 @@ void AnimationPlayer::reverse()
     }
 
     uncancel();
-
-    if (m_content) {
-        if (m_playbackRate > 0 && currentTimeInternal() > sourceEnd()) {
-            setCurrentTimeInternal(sourceEnd(), TimingUpdateOnDemand);
-            ASSERT(finished());
-        } else if (m_playbackRate < 0 && currentTimeInternal() < 0) {
-            setCurrentTimeInternal(0, TimingUpdateOnDemand);
-            ASSERT(finished());
-        }
-    }
     setPlaybackRate(-m_playbackRate);
-    unpauseInternal();
+    play();
 }
 
 void AnimationPlayer::finish(ExceptionState& exceptionState)
@@ -486,13 +476,14 @@ void AnimationPlayer::finish(ExceptionState& exceptionState)
     }
 
     uncancel();
-    m_startTime = 0;
 
-    if (m_playbackRate < 0) {
-        setCurrentTimeInternal(0, TimingUpdateOnDemand);
-    } else {
-        setCurrentTimeInternal(sourceEnd(), TimingUpdateOnDemand);
+    double newCurrentTime = m_playbackRate < 0 ? 0 : sourceEnd();
+    setCurrentTimeInternal(newCurrentTime, TimingUpdateOnDemand);
+    if (!paused()) {
+        m_startTime = calculateStartTime(newCurrentTime);
     }
+
+    m_currentTimePending = false;
     ASSERT(finished());
 }
 
@@ -532,7 +523,7 @@ void AnimationPlayer::setPlaybackRate(double playbackRate)
         return;
 
     setCompositorPending();
-    if (!finished() && !paused())
+    if (!finished() && !paused() && hasStartTime())
         m_currentTimePending = true;
 
     double storedCurrentTime = currentTimeInternal();
@@ -649,6 +640,7 @@ void AnimationPlayer::cancel()
     m_held = true;
     m_idle = true;
     m_startTime = nullValue();
+    m_currentTimePending = false;
     setCompositorPending();
 }