Implement DeferredAnimatableValue

Source/core/animation/AnimatableValue.cpp

Index: Source/core/animation/AnimatableValue.cpp
diff --git a/Source/core/animation/AnimatableValue.cpp b/Source/core/animation/AnimatableValue.cpp
index 763788093f624bd6cd513c236a73c9dcd4827904..c1dc528f6b8bb805b461833c21287c4a144e152d 100644
--- a/Source/core/animation/AnimatableValue.cpp
+++ b/Source/core/animation/AnimatableValue.cpp
@@ -31,6 +31,7 @@
 #include "config.h"
 #include "core/animation/AnimatableValue.h"
 
+#include "core/animation/AnimatableDeferredSnapshot.h"
 #include "core/animation/AnimatableNeutral.h"
 #include "core/animation/AnimatableNumber.h"
 #include "core/animation/AnimatableUnknown.h"
@@ -54,6 +55,12 @@ const AnimatableValue* AnimatableValue::neutralValue()
     return neutralSentinelValue;
 }
 
+const AnimatableValue* AnimatableValue::deferredSnapshotValue()
+{
+    static AnimatableDeferredSnapshot* deferredSnapshotSentinelValue = AnimatableDeferredSnapshot::create().leakRef();

[pdr., 2013/07/23 22:45:08]

Won't this create a new deferredSnapshotSentinelValue each time? I would have
expected something like:
if (!deferredSnapshotSentinelValue)
    deferredSnapshotSentinelValue = ...
return deferredSnapshotSentinelValue;

Additionally, why is this here and not in AnimatableDeferredSnapshot?

+    return deferredSnapshotSentinelValue;
+}
+
 PassRefPtr<AnimatableValue> AnimatableValue::interpolate(const AnimatableValue* left, const AnimatableValue* right, double fraction)
 {
     ASSERT(left);