Bug 1527210 - Drop KeyframeEffect::MaybeUpdateFrameForCompositor; r=hiro

Since bug 1524480 we set the NS_FRAME_MAY_BE_TRANSFORMED frame bit when needed
in RestyleManager::ProcessRestyledFrames so that it is now redundant to also set
it from KeyframeEffect.

Furthermore, setting frame bits from KeyframeEffect is a little fragile since it
depends on the life cycle of the KeyframeEffect which is independent of the
nsFrame. If we can avoid doing that, we probably should.

Differential Revision: https://phabricator.services.mozilla.com/D21885

--HG--
extra : moz-landing-system : lando

dom/animation/KeyframeEffect.cpp

@@ -227,7 +227,6 @@ void KeyframeEffect::SetKeyframes(nsTArray<Keyframe>&& aKeyframes,
   // style (e.g. the target element is not associated with any document).
   if (aStyle) {
     UpdateProperties(aStyle);
-    MaybeUpdateFrameForCompositor();
   }
 }
 
@@ -956,8 +955,6 @@ void KeyframeEffect::SetTarget(
       UpdateProperties(computedStyle);
     }
 
-    MaybeUpdateFrameForCompositor();
-
     RequestRestyle(EffectCompositor::RestyleType::Layer);
 
     nsAutoAnimationMutationBatch mb(mTarget->mElement->OwnerDoc());
@@ -1647,24 +1644,6 @@ bool KeyframeEffect::CanIgnoreIfNotVisible() const {
                          nsChangeHint_Hints_CanIgnoreIfNotVisible);
 }
 
-void KeyframeEffect::MaybeUpdateFrameForCompositor() {
-  nsIFrame* frame = GetStyleFrame();
-  if (!frame) {
-    return;
-  }
-
-  // FIXME: Bug 1272495: If this effect does not win in the cascade, the
-  // NS_FRAME_MAY_BE_TRANSFORMED flag should be removed when the animation
-  // will be removed from effect set or the transform keyframes are removed
-  // by setKeyframes. The latter case will be hard to solve though.
-  for (const AnimationProperty& property : mProperties) {
-    if (property.mProperty == eCSSProperty_transform) {
-      frame->AddStateBits(NS_FRAME_MAY_BE_TRANSFORMED);
-      return;
-    }
-  }
-}
-
 void KeyframeEffect::MarkCascadeNeedsUpdate() {
   if (!mTarget) {
     return;

dom/animation/KeyframeEffect.h

@@ -359,12 +359,6 @@ class KeyframeEffect : public AnimationEffect {
   // Remove the current effect target from its EffectSet.
   void UnregisterTarget();
 
-  // Update the associated frame state bits so that, if necessary, a stacking
-  // context will be created and the effect sent to the compositor.  We
-  // typically need to do this when the properties referenced by the keyframe
-  // have changed, or when the target frame might have changed.
-  void MaybeUpdateFrameForCompositor();
-
   // Looks up the ComputedStyle associated with the target element, if any.
   // We need to be careful to *not* call this when we are updating the style
   // context. That's because calling GetComputedStyle when we are in the process

layout/base/RestyleManager.cpp

@@ -1633,9 +1633,12 @@ void RestyleManager::ProcessRestyledFrames(nsStyleChangeList& aChangeList) {
           !(primaryFrame->GetStateBits() & NS_FRAME_MAY_BE_TRANSFORMED) &&
           primaryFrame->HasAnimationOfTransform()) {
         // If we have an nsChangeHint_UpdateTransformLayer hint but no
-        // corresponding frame bit, it's possible we have a transform animation
-        // with transform style 'none' that was initialized independently from
-        // this frame and associated after the fact.
+        // corresponding frame bit, we most likely have a transform animation
+        // that was added or updated after this frame was created (otherwise
+        // we would have set the frame bit when we initialized the frame)
+        // and which sets the transform to 'none' (otherwise we would have set
+        // the frame bit when we got the nsChangeHint_AddOrRemoveTransform
+        // hint).
         //
         // In that case we should set the frame bit.
         for (nsIFrame* cont = primaryFrame; cont;