Revert of Web Animations: Timeline should not advance during task execution

Source/core/dom/Document.h

Index: Source/core/dom/Document.h
diff --git a/Source/core/dom/Document.h b/Source/core/dom/Document.h
index 693a8e36ec66f9b25e619ba3605a8dfbcba98c01..d62080f04769293580358324dcd6ffa5f2590e08 100644
--- a/Source/core/dom/Document.h
+++ b/Source/core/dom/Document.h
@@ -30,7 +30,6 @@
 
 #include "bindings/v8/ExceptionStatePlaceholder.h"
 #include "bindings/v8/ScriptValue.h"
-#include "core/animation/AnimationClock.h"
 #include "core/animation/CompositorPendingAnimations.h"
 #include "core/dom/ContainerNode.h"
 #include "core/dom/DocumentEncodingData.h"
@@ -65,6 +64,7 @@
 namespace WebCore {
 
 class AXObjectCache;
+class AnimationClock;
 class Attr;
 class CDATASection;
 class CSSFontSelector;
@@ -1028,7 +1028,7 @@
     // Return a Locale for the default locale if the argument is null or empty.
     Locale& getCachedLocale(const AtomicString& locale = nullAtom);
 
-    AnimationClock& animationClock() { return m_animationClock; }
+    AnimationClock& animationClock() { return *m_animationClock; }
     AnimationTimeline& timeline() const { return *m_timeline; }
     CompositorPendingAnimations& compositorPendingAnimations() { return m_compositorPendingAnimations; }
 
@@ -1374,7 +1374,7 @@
     typedef HashMap<AtomicString, OwnPtr<Locale> > LocaleIdentifierToLocaleMap;
     LocaleIdentifierToLocaleMap m_localeCache;
 
-    AnimationClock m_animationClock;
+    OwnPtr<AnimationClock> m_animationClock;
     RefPtrWillBeMember<AnimationTimeline> m_timeline;
     CompositorPendingAnimations m_compositorPendingAnimations;