Web Animations API: Deferred computation of interpolated values

Source/core/animation/Interpolation.cpp

Index: Source/core/animation/Interpolation.cpp
diff --git a/Source/core/animation/Interpolation.cpp b/Source/core/animation/Interpolation.cpp
index 1738b817f533f9a98d670160a2a91f1ae70aaa9c..4b67a64ffa09f23c57802137dbd63ab180beaaf2 100644
--- a/Source/core/animation/Interpolation.cpp
+++ b/Source/core/animation/Interpolation.cpp
@@ -6,9 +6,8 @@
 #include "core/animation/Interpolation.h"
 
 #include "core/css/CSSCalculationValue.h"
-#include "core/css/resolver/AnimatedStyleBuilder.h"
+#include "core/css/CSSPrimitiveValue.h"
 #include "core/css/resolver/StyleBuilder.h"
-#include "core/css/resolver/StyleResolverState.h"
 
 namespace WebCore {
 
@@ -44,15 +43,18 @@ Interpolation::Interpolation(PassOwnPtrWillBeRawPtr<InterpolableValue> start, Pa
     , m_end(end)
     , m_cachedFraction(0)
     , m_cachedIteration(0)
-    , m_cachedValue(m_start->clone())
 {
-    RELEASE_ASSERT(typesMatch(m_start.get(), m_end.get()));
+    if (m_start) {
+        m_cachedValue = m_start->clone();
+        RELEASE_ASSERT(typesMatch(m_start.get(), m_end.get()));
+    }
 }
 
 void Interpolation::interpolate(int iteration, double fraction) const
 {
     if (m_cachedFraction != fraction || m_cachedIteration != iteration) {
-        m_cachedValue = m_start->interpolate(*m_end, fraction);
+        if (m_start)
+            m_cachedValue = m_start->interpolate(*m_end, fraction);
         m_cachedIteration = iteration;
         m_cachedFraction = fraction;
     }
@@ -70,16 +72,6 @@ void StyleInterpolation::trace(Visitor* visitor)
     Interpolation::trace(visitor);
 }
 
-void LegacyStyleInterpolation::apply(StyleResolverState& state) const
-{
-    AnimatedStyleBuilder::applyProperty(m_id, state, currentValue().get());
-}
-
-void LegacyStyleInterpolation::trace(Visitor* visitor)
-{
-    StyleInterpolation::trace(visitor);
-}
-
 bool LengthStyleInterpolation::canCreateFrom(const CSSValue& value)
 {
     if (value.isPrimitiveValue()) {