Supplement should have a Member to the corresponding Supplementable object (Part 1)

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

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 42 matching lines @@
     void watchCSSSelectors(const Vector<String>& selectors);
     const HeapVector<Member<StyleRule>>& watchedCallbackSelectors() const { return m_watchedCallbackSelectors; }
 
     void updateSelectorMatches(const Vector<String>& removedSelectors, const Vector<String>& addedSelectors);
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     explicit CSSSelectorWatch(Document&);
     void callbackSelectorChangeTimerFired(Timer<CSSSelectorWatch>*);
-    Document& document() const { return *m_document; }
-
-    Member<Document> m_document;
+    Document& document() const { return *host(); }

[sof, 2016/07/13 07:46:08]

assert/check for non-nullness?

[haraken, 2016/07/13 07:51:25]

Hmm, maybe CSSSelectorWatch does want to keep a strong reference to Document?
Then we should keep Member<Document>.

What we can remove is a weak reference to the host object (e.g., XXXObservers).

[sof, 2016/07/13 07:54:07]

How about going with "Member<T> m_host" ?

 
     HeapVector<Member<StyleRule>> m_watchedCallbackSelectors;
 
     // Maps a CSS selector string with a -webkit-callback property to the number
     // of matching ComputedStyle objects in this document.
     HashCountedSet<String> m_matchingCallbackSelectors;
     // Selectors are relative to m_matchingCallbackSelectors's contents at
     // the previous call to selectorMatchChanged.
     HashSet<String> m_addedSelectors;
     HashSet<String> m_removedSelectors;
 
     Timer<CSSSelectorWatch> m_callbackSelectorChangeTimer;
 
     // When an element is reparented, the new location's style is evaluated after the expriation of the relayout timer.
     // We don't want to send redundant callbacks to the embedder, so this counter lets us wait another time around the event loop.
     int m_timerExpirations;
 
     friend class CSSSelectorWatchTest;
 };
 
 } // namespace blink
 
 #endif // CSSSelectorWatch_h