Move element flags from ElementRareData to NodeRareData

Source/core/dom/Element.h

Index: Source/core/dom/Element.h
diff --git a/Source/core/dom/Element.h b/Source/core/dom/Element.h
index 29fb8ab390db2463465ee7f931a010c38e3c7eee..dacc3b14ae741ae68ce44a9abb3a2433c436fa5e 100644
--- a/Source/core/dom/Element.h
+++ b/Source/core/dom/Element.h
@@ -94,6 +94,8 @@ enum ElementFlags {
     ChildrenAffectedByForwardPositionalRules = 1 << 15,
     ChildrenAffectedByBackwardPositionalRules = 1 << 16,
 
+    NumberOfElementFlags = 17, // Required size of bitfield used to store the flags.
+
     // If any of these flags are set we cannot share style.
     ElementFlagsPreventingStyleSharing =
         ChildrenAffectedByFocus