[SVG] Implement 'discard' element

Source/core/svg/animation/SVGSMILElement.h

Index: Source/core/svg/animation/SVGSMILElement.h
diff --git a/Source/core/svg/animation/SVGSMILElement.h b/Source/core/svg/animation/SVGSMILElement.h
index 44c4fa19a4773af4b0fa2b409fd401bc85cbbe90..2c208a58a5b4c51242aeb2cf94414e0f7e9b9cb4 100644
--- a/Source/core/svg/animation/SVGSMILElement.h
+++ b/Source/core/svg/animation/SVGSMILElement.h
@@ -117,6 +117,8 @@ public:
     void dispatchPendingEvent(SMILEventSender*);
     void dispatchRepeatEvents(unsigned);
 
+    virtual bool isDiscardable() const { return false; }
+
 protected:
     void addBeginTime(SMILTime eventTime, SMILTime endTime, SMILTimeWithOrigin::Origin = SMILTimeWithOrigin::ParserOrigin);
     void addEndTime(SMILTime eventTime, SMILTime endTime, SMILTimeWithOrigin::Origin = SMILTimeWithOrigin::ParserOrigin);
@@ -241,7 +243,7 @@ private:
 inline bool isSVGSMILElement(const Node& node)
 {
     return node.hasTagName(SVGNames::setTag) || node.hasTagName(SVGNames::animateTag) || node.hasTagName(SVGNames::animateMotionTag)
-        || node.hasTagName(SVGNames::animateTransformTag) || node.hasTagName(SVGNames::animateColorTag);
+        || node.hasTagName(SVGNames::animateTransformTag) || node.hasTagName(SVGNames::animateColorTag) || node.hasTagName((SVGNames::discardTag));
 }
 
 DEFINE_NODE_TYPE_CASTS_WITH_FUNCTION(SVGSMILElement);