Adding @keyframes rules only affects TreeScope plus host.

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

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 18 matching lines @@
  */
 
 #include "core/animation/Animation.h"
 
 #include "core/animation/AnimationTimeline.h"
 #include "core/animation/CompositorPendingAnimations.h"
 #include "core/animation/KeyframeEffect.h"
 #include "core/dom/Document.h"
 #include "core/dom/ExceptionCode.h"
 #include "core/dom/StyleChangeReason.h"
+#include "core/dom/shadow/ShadowRoot.h"
 #include "core/events/AnimationPlaybackEvent.h"
 #include "core/frame/UseCounter.h"
 #include "core/inspector/InspectorInstrumentation.h"
 #include "core/inspector/InspectorTraceEvents.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/TraceEvent.h"
 #include "platform/animation/CompositorAnimationPlayer.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebCompositorSupport.h"
 #include "wtf/MathExtras.h"
@@ skipping 1030 matching lines @@
     if (suppressed)
         cancelAnimationOnCompositor();
 }
 
 void Animation::disableCompositedAnimationForTesting()
 {
     m_isCompositedAnimationDisabledForTesting = true;
     cancelAnimationOnCompositor();
 }
 
-void Animation::invalidateKeyframeEffect()
+static bool isAffectedByKeyframesFromScope(const Element& element, const TreeScope& treeScope)
+{
+    // Animated elements are affected by @keyframes rules from the same scope
+    // and from their shadow sub-trees if they are shadow hosts.
+    if (element.treeScope() == treeScope)
+        return true;
+    if (!isShadowHost(element))
+        return false;
+    if (treeScope.rootNode() == treeScope.document())
+        return false;
+    return toShadowRoot(treeScope.rootNode()).host() == element;
+}

[alancutter (OOO until 2018), 2016/09/27 06:49:50]

Nit: Move this static method to core/animation/css/CSSAnimations.h.

[rune, 2016/09/28 21:35:57]

Did you mean like patch set 4?

+
+void Animation::invalidateKeyframeEffect(const TreeScope& treeScope)
 {
     if (!m_content || !m_content->isKeyframeEffect())
         return;
 
-    toKeyframeEffect(m_content.get())->target()->setNeedsStyleRecalc(LocalStyleChange, StyleChangeReasonForTracing::create(StyleChangeReason::StyleSheetChange));
+    Element& target = *toKeyframeEffect(m_content.get())->target();
+
+    if (isAffectedByKeyframesFromScope(target, treeScope))
+        target.setNeedsStyleRecalc(LocalStyleChange, StyleChangeReasonForTracing::create(StyleChangeReason::StyleSheetChange));
 }
 
 DEFINE_TRACE(Animation)
 {
     visitor->trace(m_content);
     visitor->trace(m_timeline);
     visitor->trace(m_pendingFinishedEvent);
     visitor->trace(m_pendingCancelledEvent);
     visitor->trace(m_finishedPromise);
     visitor->trace(m_readyPromise);
     EventTargetWithInlineData::trace(visitor);
     ActiveDOMObject::trace(visitor);
 }
 
 } // namespace blink