Handle some failing DocumentOrderedMap ID lookups across tree removals.

third_party/WebKit/Source/core/dom/TreeScope.h

Index: third_party/WebKit/Source/core/dom/TreeScope.h
diff --git a/third_party/WebKit/Source/core/dom/TreeScope.h b/third_party/WebKit/Source/core/dom/TreeScope.h
index 88a3a756d4e0c3af496985634ed2a8155604c520..bf26f0df5776cbed62c7517f491702c582617031 100644
--- a/third_party/WebKit/Source/core/dom/TreeScope.h
+++ b/third_party/WebKit/Source/core/dom/TreeScope.h
@@ -143,6 +143,17 @@ public:
     ScopedStyleResolver& ensureScopedStyleResolver();
     void clearScopedStyleResolver();
 
+#if ENABLE(ASSERT)
+    class RemoveScope {
+        STACK_ALLOCATED();
+    public:
+        explicit RemoveScope(ContainerNode*);

[esprehn, 2016/01/05 07:48:33]

reference, this should also be nested inside the map, not in the TreeScope.

+        ~RemoveScope();
+    private:
+        RawPtrWillBeMember<DocumentOrderedMap> m_idMap;
+    };
+#endif
+
 protected:
     TreeScope(ContainerNode&, Document&);
     TreeScope(Document&);
@@ -162,6 +173,8 @@ protected:
     void setNeedsStyleRecalcForViewportUnits();
 
 private:
+    friend class RemoveScope;
+
 #if !ENABLE(OILPAN)
     virtual void dispose() { }