Animation: FilterStyleInterpolation for animating filter

Source/core/animation/StringKeyframe.cpp

Index: Source/core/animation/StringKeyframe.cpp
diff --git a/Source/core/animation/StringKeyframe.cpp b/Source/core/animation/StringKeyframe.cpp
index a654909c3cc86416f29376f2ec8c2a7616cf5f5e..0ab351e18dd700b7f17412a82054945e574766bd 100644
--- a/Source/core/animation/StringKeyframe.cpp
+++ b/Source/core/animation/StringKeyframe.cpp
@@ -12,6 +12,7 @@
 #include "core/animation/DefaultSVGInterpolation.h"
 #include "core/animation/DeferredLegacyStyleInterpolation.h"
 #include "core/animation/DoubleStyleInterpolation.h"
+#include "core/animation/FilterStyleInterpolation.h"
 #include "core/animation/ImageSliceStyleInterpolation.h"
 #include "core/animation/ImageStyleInterpolation.h"
 #include "core/animation/IntegerOptionalIntegerSVGInterpolation.h"
@@ -391,6 +392,16 @@ PassRefPtrWillBeRawPtr<Interpolation> StringKeyframe::CSSPropertySpecificKeyfram
         break;
     }
 
+    case CSSPropertyWebkitFilter: {
+        RefPtrWillBeRawPtr<Interpolation> interpolation = FilterStyleInterpolation::maybeCreateList(*fromCSSValue, *toCSSValue, property);
+        if (interpolation)
+            return interpolation.release();
+
+        // FIXME: Support drop shadow interpolation.
+        fallBackToLegacy = true;
+        break;
+    }
+
     default:
         // Fall back to LegacyStyleInterpolation.
         fallBackToLegacy = true;