Adding @keyframes rules only affects TreeScope plus host.

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

Index: third_party/WebKit/Source/core/animation/Animation.cpp
diff --git a/third_party/WebKit/Source/core/animation/Animation.cpp b/third_party/WebKit/Source/core/animation/Animation.cpp
index b34fac998d20df5135d6d6c6536ca9d01492b56b..c16097004d21dc3ea3c0c37e99412918d3b36cda 100644
--- a/third_party/WebKit/Source/core/animation/Animation.cpp
+++ b/third_party/WebKit/Source/core/animation/Animation.cpp
@@ -36,6 +36,7 @@
 #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"
@@ -1086,12 +1087,28 @@ void Animation::disableCompositedAnimationForTesting()
     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)