Bug 1150810 part 9 - Add relevant animations to timeline; r=jwatt

We only store relevant animations on the timeline. Relevant animations are
any animations that are running or yet to run ("current animations") or
which have finished but are still applying a fill mode ("in effect animations").

AnimationTimeline.getAnimations() only ever returns relevant animations so
this is the minimum set we need to keep track of. Keeping track of any more
than this would prevent us from garbage-collecting any no longer relevant
animations since we keep a strong reference to this animations.

The reason we keep a strong reference is that if an animation is attached to
a timeline, even if there are no references to it from script or markup it
needs to be kept alive in order to dispatch events or resolve promises. An
irrelevant animation however is not going to do either of these things without
outside intervention so we don't need to keep it alive.

--HG--
extra : commitid : WLEUccOqAk
extra : rebase_source : 5c3c987d6c95ca7072c6178349dc113d2f1e5053

dom/animation/Animation.cpp

@@ -62,6 +62,10 @@ Animation::SetTimeline(AnimationTimeline* aTimeline)
     return;
   }
 
+  if (mTimeline) {
+    mTimeline->RemoveAnimation(*this);
+  }
+
   mTimeline = aTimeline;
 
   // FIXME(spec): Once we implement the seeking defined in the spec
@@ -788,6 +792,35 @@ Animation::UpdateTiming(SeekFlag aSeekFlag)
   // can change the current time, which is used by the latter.
   UpdateFinishedState(aSeekFlag);
   UpdateEffect();
+
+  // Unconditionally Add/Remove from the timeline. This is ok because if the
+  // animation has already been added/removed (which will be true more often
+  // than not) the work done by AnimationTimeline/DocumentTimeline is still
+  // negligible and its easier than trying to detect whenever we are switching
+  // to/from being relevant.
+  //
+  // We need to do this after calling UpdateEffect since it updates some
+  // cached state used by IsRelevant.
+  //
+  // Note that we only store relevant animations on the timeline since they
+  // are the only ones that need ticks and are the only ones returned from
+  // AnimationTimeline::GetAnimations. Storing any more than that would mean
+  // that we fail to garbage collect irrelevant animations since the timeline
+  // keeps a strong reference to each animation.
+  //
+  // Once we tick animations from the their timeline, and once we expect
+  // timelines to go in and out of being inactive, we will also need to store
+  // non-idle animations that are waiting for their timeline to become active
+  // on their timeline (as otherwise once the timeline becomes active it will
+  // have no way of notifying its animations). For now, however, we can
+  // simply store just the relevant animations.
+  if (mTimeline) {
+    if (IsRelevant()) {
+      mTimeline->AddAnimation(*this);
+    } else {
+      mTimeline->RemoveAnimation(*this);
+    }
+  }
 }
 
 void