(WIP) Paint invalidation for slimming paint v2

Source/core/paint/PaintPhase.h

Index: Source/core/paint/PaintPhase.h
diff --git a/Source/core/paint/PaintPhase.h b/Source/core/paint/PaintPhase.h
index 7c3ce1a3060204bbb689cf4bb61c7497d38ab197..d8a751cf76340f556b6717d5dc477db317d6e99d 100644
--- a/Source/core/paint/PaintPhase.h
+++ b/Source/core/paint/PaintPhase.h
@@ -38,6 +38,7 @@ namespace blink {
  */
 
 enum PaintPhase {
+    PaintPhaseInvalidation = -1,
     PaintPhaseBlockBackground = 0,
     PaintPhaseChildBlockBackground = 1,
     PaintPhaseChildBlockBackgrounds = 2,
@@ -52,7 +53,8 @@ enum PaintPhase {
     PaintPhaseMask = 11,
     PaintPhaseClippingMask = 12,
     PaintPhaseMax = PaintPhaseClippingMask,
-    // These values must be kept in sync with DisplayItem::Type and DisplayItem::typeAsDebugString().
+    // These values except PaintPhaseInvalidation must be kept in sync with
+    // DisplayItem::Type and DisplayItem::typeAsDebugString().
 };
 
 // Those flags are meant as global tree operations. This means