Web Animations: Support animation of flood-opacity

Source/core/animation/css/CSSAnimatableValueFactory.cpp

Index: Source/core/animation/css/CSSAnimatableValueFactory.cpp
diff --git a/Source/core/animation/css/CSSAnimatableValueFactory.cpp b/Source/core/animation/css/CSSAnimatableValueFactory.cpp
index 66dc96ccda959e21972f7864c6a388cd10723c13..5c21138428e55cb020858c78e0ee0e8ef5c39a35 100644
--- a/Source/core/animation/css/CSSAnimatableValueFactory.cpp
+++ b/Source/core/animation/css/CSSAnimatableValueFactory.cpp
@@ -224,6 +224,8 @@ PassRefPtr<AnimatableValue> CSSAnimatableValueFactory::create(CSSPropertyID prop
         return createFromLength(style->flexBasis(), style);
     case CSSPropertyFloodColor:
         return createFromColor(property, style);
+    case CSSPropertyFloodOpacity:
+        return createFromDouble(style->floodOpacity());
     case CSSPropertyFontSize:
         // Must pass a specified size to setFontSize if Text Autosizing is enabled, but a computed size
         // if text zoom is enabled (if neither is enabled it's irrelevant as they're probably the same).