Web Animations: Make AnimationPlaybackEvent's members null by default

Whilst the code did correctly check whether the members of
AnimationPlaybackEventInit were null, the AnimationPlaybackEvent
constructor was setting them to 0.0 as a default value, which is
incorrect via the spec:

https://drafts.csswg.org/web-animations-1/#the-animationplaybackevent-interface

This CL also converts the class members to use WTF::Optional to
clearly distinguish between them being set and not set.

Bug: 827572
Change-Id: I471666a022963dd19f8a74eaebafeeebf4e96c66
Reviewed-on: https://chromium-review.googlesource.com/988339Reviewed-by: Xida Chen <xidachen@chromium.org>
Reviewed-by: dsinclair <dsinclair@chromium.org>
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547715}

third_party/WebKit/LayoutTests/external/wpt/web-animations/interfaces/AnimationPlaybackEvent/constructor-expected.txt

-This is a testharness.js-based test.
-FAIL Event created without an event parameter has null time values assert_equals: expected (object) null but got (number) 0
-PASS Created event reflects times specified in constructor
-Harness: the test ran to completion.
-

third_party/WebKit/Source/core/events/AnimationPlaybackEvent.cpp

@@ -16,7 +16,7 @@ AnimationPlaybackEvent::AnimationPlaybackEvent(const AtomicString& type,
 AnimationPlaybackEvent::AnimationPlaybackEvent(
     const AtomicString& type,
     const AnimationPlaybackEventInit& initializer)
-    : Event(type, initializer), current_time_(0.0), timeline_time_(0.0) {
+    : Event(type, initializer) {
   if (initializer.hasCurrentTime())
     current_time_ = initializer.currentTime();
   if (initializer.hasTimelineTime())
@@ -26,23 +26,13 @@ AnimationPlaybackEvent::AnimationPlaybackEvent(
 AnimationPlaybackEvent::~AnimationPlaybackEvent() = default;
 
 double AnimationPlaybackEvent::currentTime(bool& is_null) const {
-  double result = currentTime();
-  is_null = std::isnan(result);
-  return result;
-}
-
-double AnimationPlaybackEvent::currentTime() const {
-  return current_time_;
+  is_null = !current_time_.has_value();
+  return current_time_.value_or(0);
 }
 
 double AnimationPlaybackEvent::timelineTime(bool& is_null) const {
-  double result = timelineTime();
-  is_null = std::isnan(result);
-  return result;
-}
-
-double AnimationPlaybackEvent::timelineTime() const {
-  return timeline_time_;
+  is_null = !timeline_time_.has_value();
+  return timeline_time_.value_or(0);
 }
 
 const AtomicString& AnimationPlaybackEvent::InterfaceName() const {

third_party/WebKit/Source/core/events/AnimationPlaybackEvent.h

@@ -7,6 +7,7 @@
 
 #include "core/dom/events/Event.h"
 #include "core/events/AnimationPlaybackEventInit.h"
+#include "platform/wtf/Optional.h"
 
 namespace blink {
 
@@ -28,9 +29,7 @@ class AnimationPlaybackEvent final : public Event {
   ~AnimationPlaybackEvent() override;
 
   double currentTime(bool& is_null) const;
-  double currentTime() const;
   double timelineTime(bool& is_null) const;
-  double timelineTime() const;
 
   const AtomicString& InterfaceName() const override;
 
@@ -43,8 +42,8 @@ class AnimationPlaybackEvent final : public Event {
   AnimationPlaybackEvent(const AtomicString&,
                          const AnimationPlaybackEventInit&);
 
-  double current_time_;
-  double timeline_time_;
+  WTF::Optional<double> current_time_;
+  WTF::Optional<double> timeline_time_;
 };
 
 }  // namespace blink