[Slimming Paint] Implement deferred SVG filters

Source/platform/graphics/paint/DisplayItem.cpp

Index: Source/platform/graphics/paint/DisplayItem.cpp
diff --git a/Source/platform/graphics/paint/DisplayItem.cpp b/Source/platform/graphics/paint/DisplayItem.cpp
index c5cddddfccc8ff82b53b60852833d185003578be..d84b93f07a90e0eae21e71b9b1d19d5df9c96678 100644
--- a/Source/platform/graphics/paint/DisplayItem.cpp
+++ b/Source/platform/graphics/paint/DisplayItem.cpp
@@ -78,6 +78,7 @@ WTF::String DisplayItem::typeAsDebugString(DisplayItem::Type type)
     case PageWidgetDelegateClip: return "PageWidgetDelegateClip";
     case PageWidgetDelegateBackgroundFallback: return "PageWidgetDelegateBackgroundFallback";
     case ViewBackground: return "ViewBackground";
+    case SVGFilter: return "SVGFilter";
     }
     ASSERT_NOT_REACHED();
     return "Unknown";