Prepare for responsive CSS animations.

Source/core/animation/KeyframeEffectModel.cpp

Index: Source/core/animation/KeyframeEffectModel.cpp
diff --git a/Source/core/animation/KeyframeEffectModel.cpp b/Source/core/animation/KeyframeEffectModel.cpp
index fc1f34f527f23625c0e39c8a4883b41ff85e1b13..9356b8701f6b3409f7a4bf1a4108f9acb53e0e26 100644
--- a/Source/core/animation/KeyframeEffectModel.cpp
+++ b/Source/core/animation/KeyframeEffectModel.cpp
@@ -33,6 +33,9 @@
 
 #include "core/StylePropertyShorthand.h"
 #include "core/animation/AnimationNode.h"
+#include "core/animation/css/CSSAnimatableValueFactory.h"
+#include "core/animation/css/CSSPropertyEquality.h"
+#include "core/css/resolver/StyleResolver.h"
 #include "platform/animation/AnimationUtilities.h"
 #include "platform/geometry/FloatBox.h"
 #include "platform/transforms/TransformationMatrix.h"
@@ -60,6 +63,50 @@ void KeyframeEffectModelBase::sample(int iteration, double fraction, double iter
     return m_interpolationEffect->getActiveInterpolations(fraction, iterationDuration, result);
 }
 
+void KeyframeEffectModelBase::snapshotCompositableProperties(const Element* element, const RenderStyle& style)
+{
+    if (affects(CSSPropertyOpacity))
+        snapshotCompositableProperty(CSSPropertyOpacity, element, style);
+    if (affects(CSSPropertyTransform))
+        snapshotCompositableProperty(CSSPropertyTransform, element, style);
+    if (affects(CSSPropertyWebkitFilter))
+        snapshotCompositableProperty(CSSPropertyWebkitFilter, element, style);
+}
+
+bool KeyframeEffectModelBase::snapshotCompositablePropertiesIfNeeded(const Element* element, const RenderStyle& oldStyle, const RenderStyle& newStyle)
+{
+    bool changed = false;
+
+    if (!CSSPropertyEquality::propertiesEqual(CSSPropertyOpacity, oldStyle, newStyle) && affects(CSSPropertyOpacity)) {
+        snapshotCompositableProperty(CSSPropertyOpacity, element, newStyle);
+        changed = true;
+    }
+
+    if (!CSSPropertyEquality::propertiesEqual(CSSPropertyTransform, oldStyle, newStyle) && affects(CSSPropertyTransform)) {
+        snapshotCompositableProperty(CSSPropertyTransform, element, newStyle);
+        changed = true;
+    }
+
+    if (!CSSPropertyEquality::propertiesEqual(CSSPropertyWebkitFilter, oldStyle, newStyle) && affects(CSSPropertyWebkitFilter)) {
+        snapshotCompositableProperty(CSSPropertyWebkitFilter, element, newStyle);
+        changed = true;
+    }
+
+    return changed;
+}
+
+void KeyframeEffectModelBase::snapshotCompositableProperty(CSSPropertyID property, const Element* element, const RenderStyle& style)
+{
+    auto& keyframes = m_keyframeGroups->get(property)->m_keyframes;
+    for (size_t i = 0; i < keyframes.size(); i++) {
+        auto& keyframe = toStringPropertySpecificKeyframe(*keyframes[i]);
+        if (!keyframe.value())
+            keyframe.setAnimatableValue(CSSAnimatableValueFactory::create(property, style));
+        else if (!keyframe.getAnimatableValue())
+            keyframe.setAnimatableValue(StyleResolver::createAnimatableValueSnapshot(const_cast<Element&>(*element), property, *keyframe.value()));
+    }
+}
+
 KeyframeEffectModelBase::KeyframeVector KeyframeEffectModelBase::normalizedKeyframes(const KeyframeVector& keyframes)
 {
     double lastOffset = 0;
@@ -140,9 +187,9 @@ void KeyframeEffectModelBase::ensureInterpolationEffect(Element* element) const
 
     for (const auto& entry : *m_keyframeGroups) {
         const PropertySpecificKeyframeVector& keyframes = entry.value->keyframes();
-        ASSERT(keyframes[0]->composite() == AnimationEffect::CompositeReplace);
+        ASSERT(keyframes[0]->composite() == AnimationEffect::CompositeReplace || keyframes[0]->composite() == AnimationEffect::CompositeAdd);
         for (size_t i = 0; i < keyframes.size() - 1; i++) {
-            ASSERT(keyframes[i + 1]->composite() == AnimationEffect::CompositeReplace);
+            ASSERT(keyframes[i + 1]->composite() == AnimationEffect::CompositeReplace || keyframes[i + 1]->composite() == AnimationEffect::CompositeAdd);
             double applyFrom = i ? keyframes[i]->offset() : (-std::numeric_limits<double>::infinity());
             double applyTo = i == keyframes.size() - 2 ? std::numeric_limits<double>::infinity() : keyframes[i + 1]->offset();
             if (applyTo == 1)