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 b5b7c95da88d3a821f16423551b29bcc357865c5..f79a4145a95738f22dbad723d40b399c0932e782 100644
--- a/Source/core/animation/StringKeyframe.cpp
+++ b/Source/core/animation/StringKeyframe.cpp
@@ -10,6 +10,7 @@
 #include "core/animation/ConstantStyleInterpolation.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/LegacyStyleInterpolation.h"
@@ -356,6 +357,16 @@ PassRefPtrWillBeRawPtr<Interpolation> StringKeyframe::PropertySpecificKeyframe::
         break;
     }
 
+    case CSSPropertyWebkitFilter: {
+        RefPtrWillBeRawPtr<Interpolation> interpolation = FilterStyleInterpolation::maybeCreate(*fromCSSValue, *toCSSValue, property);
+        if (interpolation)
+            return interpolation.release();
+
+        // FIXME: Support drop shadow interpolation.
+        fallBackToLegacy = true;
+        break;
+    }
+
     default:
         // Fall back to LegacyStyleInterpolation.
         fallBackToLegacy = true;