Oilpan: move custom element objects to the heap.

Source/core/dom/custom/CustomElementObserver.cpp

Index: Source/core/dom/custom/CustomElementObserver.cpp
diff --git a/Source/core/dom/custom/CustomElementObserver.cpp b/Source/core/dom/custom/CustomElementObserver.cpp
index 94247fccecc50495716d4ac701a9ec1abe1462fc..3988dfc1e805ef4e574d7c4da652ba3336735ff5 100644
--- a/Source/core/dom/custom/CustomElementObserver.cpp
+++ b/Source/core/dom/custom/CustomElementObserver.cpp
@@ -31,12 +31,23 @@
 #include "config.h"
 #include "core/dom/custom/CustomElementObserver.h"
 
+#include "core/dom/Element.h"
+
 namespace WebCore {
 
-CustomElementObserver::ElementObserverMap& CustomElementObserver::elementObservers()
+// Maps elements to the observer watching them. At most one per
+// element at a time.
+typedef WillBeHeapHashMap<RawPtrWillBeWeakMember<Element>, RawPtrWillBeMember<CustomElementObserver> > ElementObserverMap;

[haraken, 2014/05/26 15:40:23]

I think you need to remove the following lines from Element's destructor:

Element::~Element() {
  ...;
  if (isCustomElement())
    CustomElement::wasDestroyed(this);
  ...;
}

CustomElement::wasDestroyed calls
CustomElementUpgradeCandidateMap::elementWasDestroyed and thus touches on-heap
objects. I guess this will cause an ASan issue.

[sof, 2014/05/26 16:41:08]

Very good catch; made it conditional on !ENABLE(OILPAN).

The weak reference on the other side will remove/unregister the object during
the same GC.

[sof, 2014/05/26 19:25:37]

Just to continue that thought & looking at details some more.. the weak
reference to the Element is cleared out before the sweep and Element
finalization, so CustomElementObserver::notifyElementWasDestroyed() will return
early and no possibly-finalized heap objects will be touched here.

So, while clearly wrong to trigger the wasDestroyed() call in ~Element, it is
not unsafe, just redundant (with the current implementation.)

+
+static ElementObserverMap& elementObservers()
 {
+#if ENABLE(OILPAN)
+    DEFINE_STATIC_LOCAL(Persistent<ElementObserverMap>, map, (new ElementObserverMap()));
+    return *map;
+#else
     DEFINE_STATIC_LOCAL(ElementObserverMap, map, ());
     return map;
+#endif
 }
 
 void CustomElementObserver::notifyElementDidFinishParsingChildren(Element* element)