Check slot's distribution state more strictly

third_party/WebKit/Source/core/html/HTMLSlotElement.h

Index: third_party/WebKit/Source/core/html/HTMLSlotElement.h
diff --git a/third_party/WebKit/Source/core/html/HTMLSlotElement.h b/third_party/WebKit/Source/core/html/HTMLSlotElement.h
index d66676a8d6154332d6671b602ce07b423e744ea2..828099919c1145bf7ecd888e6d359ed7fa495e6e 100644
--- a/third_party/WebKit/Source/core/html/HTMLSlotElement.h
+++ b/third_party/WebKit/Source/core/html/HTMLSlotElement.h
@@ -56,7 +56,7 @@ public:
     void appendAssignedNode(Node&);
     void appendDistributedNode(Node&);
     void appendDistributedNodesFrom(const HTMLSlotElement& other);
-    void clearDistribution();
+    void willUpdateDistribution();

[kochi, 2016/03/04 03:49:07]

nit: Looking at usages, I'd think renaming
willUpdateDistribution/didUpdateDistribution to
startUpdateDistribution()/finishUpdateDistribution()) is better, but it's up to
you.

 
     bool hasSlotChangeEventListener();
 
@@ -74,11 +74,13 @@ private:
     HTMLSlotElement(Document&);
 
     enum DistributionState {
-        DistributionReset,
+        DistributionOnGoing,
+        DistributionDone,
         DistributionChanged,
         DistributionUnchanged
     };
 
+    void clearDistribution();
     void childrenChanged(const ChildrenChange&) final;
     InsertionNotificationRequest insertedInto(ContainerNode*) final;
     void removedFrom(ContainerNode*) final;