Sync SMIL timeline when inserting into document

SMILTimeContainer::Elapsed() could return a negative time, this
should not be possible anymore. Since if you now reinsert
the SVG, it should resync.

Nothing else should have changed.

Bug: 996196
Change-Id: Id75b1604b8a087c5c046f842273cd8355075cb56
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1763420
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Reviewed-by: Fredrik Söderquist <fs@opera.com>
Auto-Submit: Edvard Thörnros <edvardt@opera.com>
Cr-Commit-Position: refs/heads/master@{#689016}

third_party/blink/renderer/core/svg/animation/smil_time_container.cc

@@ -257,6 +257,17 @@ void SMILTimeContainer::SetElapsed(double elapsed) {
   UpdateAnimationsAndScheduleFrameIfNeeded(elapsed, true);
 }
 
+void SMILTimeContainer::ResetReferenceTime() {
+  DCHECK(IsStarted());
+  if (!GetDocument().IsActive())
+    return;
+
+  if (!HandleAnimationPolicy(kRestartOnceTimerIfNotPaused))
+    return;
+
+  SynchronizeToDocumentTimeline();
+}
+
 void SMILTimeContainer::ScheduleAnimationFrame(double delay_time) {
   DCHECK(std::isfinite(delay_time));
   DCHECK(IsTimelineRunning());

third_party/blink/renderer/core/svg/animation/smil_time_container.h

@@ -76,6 +76,8 @@ class SMILTimeContainer : public GarbageCollectedFinalized<SMILTimeContainer> {
 
   void Trace(blink::Visitor*);
 
+  void ResetReferenceTime();
+
  private:
   enum FrameSchedulingState {
     // No frame scheduled.

third_party/blink/renderer/core/svg/svg_svg_element.cc

@@ -520,9 +520,12 @@ Node::InsertionNotificationRequest SVGSVGElement::InsertedInto(
     // the load event, but if we miss that train (deferred programmatic
     // element insertion for example) we need to initialize the time container
     // here.
-    if (!GetDocument().Parsing() && GetDocument().LoadEventFinished() &&
-        !TimeContainer()->IsStarted())
-      TimeContainer()->Start();
+    if (!GetDocument().Parsing() && GetDocument().LoadEventFinished()) {
+      if (!TimeContainer()->IsStarted())
+        TimeContainer()->Start();
+      else
+        TimeContainer()->ResetReferenceTime();
+    }
   }
   return SVGGraphicsElement::InsertedInto(root_parent);
 }