[Slimming Paint] Add *FilterDisplayItem type for slimming paint

Source/core/paint/ViewDisplayList.cpp

Index: Source/core/paint/ViewDisplayList.cpp
diff --git a/Source/core/paint/ViewDisplayList.cpp b/Source/core/paint/ViewDisplayList.cpp
index 4c3cb1a37265991dfa9e0e7c7ad64e2eb911c86a..ab0520973a2cad59c356fc3cdd7111ea28a8e3fa 100644
--- a/Source/core/paint/ViewDisplayList.cpp
+++ b/Source/core/paint/ViewDisplayList.cpp
@@ -146,6 +146,8 @@ WTF::String DisplayItem::typeAsDebugString(DisplayItem::Type type)
     case DisplayItem::ClipLayerFragmentSelection: return "ClipLayerFragmentSelection";
     case DisplayItem::ClipLayerFragmentChildBlockBackgrounds: return "ClipLayerFragmentChildBlockBackgrounds";
     case DisplayItem::EndClip: return "EndClip";
+    case DisplayItem::BeginFilter: return "BeginFilter";
+    case DisplayItem::EndFilter: return "EndFilter";
     }
     ASSERT_NOT_REACHED();
     return "Unknown";