Web Animations: Early-exit from setCurrentTime if new time is null

The spec says that setting the current time to null should throw if the
existing currentTime is non-null, or do nothing otherwise.

Bug: 818196
Change-Id: Iac89e46d6b884c924c88b603fbec77b61a337ce2
Reviewed-on: https://chromium-review.googlesource.com/946050Reviewed-by: Xida Chen <xidachen@chromium.org>
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542682}

third_party/WebKit/LayoutTests/external/wpt/web-animations/timing-model/animations/setting-the-current-time-of-an-animation-expected.txt

 This is a testharness.js-based test.
+FAIL Setting the current time of a pending animation to unresolved does not throw a TypeError Failed to set the 'currentTime' property on 'Animation': currentTime may not be changed from resolved to unresolved
+PASS Setting the current time of a playing animation to unresolved throws a TypeError
+PASS Setting the current time of a paused animation to unresolved throws a TypeError
 FAIL Setting the current time of a pausing animation applies a pending playback rate assert_true: expected true got undefined
 Harness: the test ran to completion.
 

third_party/WebKit/LayoutTests/external/wpt/web-animations/timing-model/animations/setting-the-current-time-of-an-animation.html

@@ -11,6 +11,39 @@
 <script>
 'use strict';
 
+test(t => {
+  const anim = new Animation();
+  assert_equals(anim.playState, 'idle');
+  assert_equals(anim.currentTime, null);
+
+  // This should not throw because the currentTime is already null.
+  anim.currentTime = null;
+}, 'Setting the current time of a pending animation to unresolved does not'
+   + ' throw a TypeError');
+
+promise_test(async t => {
+  const anim = createDiv(t).animate(null, 100 * MS_PER_SEC);
+  await anim.ready;
+
+  assert_greater_than_equal(anim.currentTime, 0);
+  assert_throws({ name: 'TypeError' }, () => {
+    anim.currentTime = null;
+  });
+}, 'Setting the current time of a playing animation to unresolved throws a'
+   + ' TypeError');
+
+promise_test(async t => {
+  const anim = createDiv(t).animate(null, 100 * MS_PER_SEC);
+  await anim.ready;
+  anim.pause();
+
+  assert_greater_than_equal(anim.currentTime, 0);
+  assert_throws({ name: 'TypeError' }, () => {
+    anim.currentTime = null;
+  });
+}, 'Setting the current time of a paused animation to unresolved throws a'
+   + ' TypeError');
+
 promise_test(async t => {
   const anim = createDiv(t).animate(null, 100 * MS_PER_SEC);
   await anim.ready;

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

@@ -164,9 +164,22 @@ bool Animation::Limited(double current_time) const {
          (playback_rate_ > 0 && current_time >= EffectEnd());
 }
 
-void Animation::setCurrentTime(double new_current_time, bool is_null) {
+void Animation::setCurrentTime(double new_current_time,
+                               bool is_null,
+                               ExceptionState& exception_state) {
   PlayStateUpdateScope update_scope(*this, kTimingUpdateOnDemand);
 
+  // Step 1. of the procedure to silently set the current time of an
+  // animation states that we abort if the new time is null.
+  if (is_null) {
+    // If the current time is resolved, then throw a TypeError.
+    if (!IsNull(CurrentTimeInternal())) {
+      exception_state.ThrowTypeError(
+          "currentTime may not be changed from resolved to unresolved");
+    }
+    return;
+  }
+
   if (PlayStateInternal() == kIdle)
     paused_ = true;
 
@@ -455,6 +468,7 @@ double Animation::CalculateStartTime(double current_time) const {
 }
 
 double Animation::CalculateCurrentTime() const {
+  // TODO(crbug.com/818196): By spec, this should be unresolved, not 0.
   if (IsNull(start_time_) || !timeline_)
     return 0;
   return (timeline_->EffectiveTime() - start_time_) * playback_rate_;

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

@@ -112,7 +112,9 @@ class CORE_EXPORT Animation final : public EventTargetWithInlineData,
 
   double currentTime(bool& is_null);
   double currentTime();
-  void setCurrentTime(double new_current_time, bool is_null);
+  void setCurrentTime(double new_current_time,
+                      bool is_null,
+                      ExceptionState& = ASSERT_NO_EXCEPTION);
 
   double CurrentTimeInternal() const;
   double UnlimitedCurrentTimeInternal() const;

third_party/WebKit/Source/core/animation/Animation.idl

@@ -43,7 +43,7 @@ enum AnimationPlayState { "idle", "pending", "running", "paused", "finished" };
     [RuntimeEnabled=WebAnimationsAPI] attribute AnimationEffectReadOnly? effect;
     [RuntimeEnabled=WebAnimationsAPI] readonly attribute AnimationTimeline? timeline;
     [Measure] attribute double?    startTime;
-    [Measure] attribute double?    currentTime;
+    [Measure, RaisesException=Setter] attribute double?    currentTime;
     [Measure] attribute double     playbackRate;
     [Measure] readonly attribute AnimationPlayState playState;
     [Measure, RaisesException] void finish();