Web Animations: give ComputedEffectTiming::endTime a lower bound of 0

The spec defined the calculation clearly, but we had missed the
lower bound:

https://drafts.csswg.org/web-animations-1/#end-time

Bug: 827623
Change-Id: If7ae487d0be09753b2357f1379a2f225a7861bae
Reviewed-on: https://chromium-review.googlesource.com/989428Reviewed-by: Xida Chen <xidachen@chromium.org>
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547685}

third_party/WebKit/LayoutTests/external/wpt/web-animations/interfaces/AnimationEffect/getComputedTiming-expected.txt

-This is a testharness.js-based test.
-PASS values of getComputedTiming() when a KeyframeEffect is constructed without any KeyframeEffectOptions object
-PASS values of getComputedTiming() when a KeyframeEffect is constructed by an empty KeyframeEffectOptions object
-PASS values of getComputedTiming() when a KeyframeEffect is constructed by a normal KeyframeEffectOptions object
-PASS values of getComputedTiming() when a KeyframeEffect is constructed by a double value
-PASS values of getComputedTiming() when a KeyframeEffect is constructed by +Infinity
-PASS values of getComputedTiming() when a KeyframeEffect is constructed by an Infinity duration
-PASS values of getComputedTiming() when a KeyframeEffect is constructed by an auto duration
-PASS values of getComputedTiming() when a KeyframeEffect is constructed by an Infinity iterations
-PASS values of getComputedTiming() when a KeyframeEffect is constructed by an auto fill
-PASS values of getComputedTiming() when a KeyframeEffect is constructed by a forwards fill
-PASS getComputedTiming().activeDuration for an empty KeyframeEffectOptions object
-PASS getComputedTiming().activeDuration for a non-zero duration and default iteration count
-PASS getComputedTiming().activeDuration for a non-zero duration and integral iteration count
-PASS getComputedTiming().activeDuration for a non-zero duration and fractional iteration count
-PASS getComputedTiming().activeDuration for an non-zero duration and infinite iteration count
-PASS getComputedTiming().activeDuration for an non-zero duration and zero iteration count
-PASS getComputedTiming().activeDuration for a zero duration and default iteration count
-PASS getComputedTiming().activeDuration for a zero duration and fractional iteration count
-PASS getComputedTiming().activeDuration for a zero duration and infinite iteration count
-PASS getComputedTiming().activeDuration for a zero duration and zero iteration count
-PASS getComputedTiming().activeDuration for an infinite duration and default iteration count
-PASS getComputedTiming().activeDuration for an infinite duration and zero iteration count
-PASS getComputedTiming().activeDuration for an infinite duration and fractional iteration count
-PASS getComputedTiming().activeDuration for an infinite duration and infinite iteration count
-PASS getComputedTiming().endTime for an empty KeyframeEffectOptions object
-PASS getComputedTiming().endTime for a non-zero duration and default iteration count
-PASS getComputedTiming().endTime for a non-zero duration and non-default iteration count
-PASS getComputedTiming().endTime for a non-zero duration and non-zero delay
-PASS getComputedTiming().endTime for a non-zero duration, non-zero delay and non-default iteration
-PASS getComputedTiming().endTime for an infinite iteration count
-PASS getComputedTiming().endTime for an infinite duration
-PASS getComputedTiming().endTime for an infinite duration and delay
-PASS getComputedTiming().endTime for an infinite duration and negative delay
-PASS getComputedTiming().endTime for an non-zero duration and negative delay
-FAIL getComputedTiming().endTime for an non-zero duration and negative delay greater than active duration assert_equals: expected 0 but got -1000
-FAIL getComputedTiming().endTime for a zero duration and negative delay assert_equals: expected 0 but got -1000
-Harness: the test ran to completion.
-

third_party/WebKit/Source/core/animation/AnimationEffect.cpp

@@ -85,6 +85,13 @@ double AnimationEffect::ActiveDurationInternal() const {
   return result;
 }
 
+double AnimationEffect::EndTimeInternal() const {
+  // Per the spec, the end time has a lower bound of 0.0:
+  // https://drafts.csswg.org/web-animations-1/#end-time
+  return std::max(
+      timing_.start_delay + ActiveDurationInternal() + timing_.end_delay, 0.0);
+}
+
 void AnimationEffect::UpdateSpecifiedTiming(const Timing& timing) {
   // FIXME: Test whether the timing is actually different?
   timing_ = timing;

third_party/WebKit/Source/core/animation/AnimationEffect.h

@@ -108,10 +108,7 @@ class CORE_EXPORT AnimationEffect : public ScriptWrappable {
 
   double IterationDuration() const;
   double ActiveDurationInternal() const;
-  double EndTimeInternal() const {
-    return SpecifiedTiming().start_delay + ActiveDurationInternal() +
-           SpecifiedTiming().end_delay;
-  }
+  double EndTimeInternal() const;
 
   const Timing& SpecifiedTiming() const { return timing_; }
   virtual AnimationEffectTimingReadOnly* timing();