Oilpan:Allow custom handling of classes that contain weak pointers that are embedded in collections.

Source/platform/heap/Handle.h

Index: Source/platform/heap/Handle.h
diff --git a/Source/platform/heap/Handle.h b/Source/platform/heap/Handle.h
index d3872b02be0e526a2361b54a410d1922ab06c8d4..a01460dcaafee60258a21d6a4f7c3cf474d82935 100644
--- a/Source/platform/heap/Handle.h
+++ b/Source/platform/heap/Handle.h
@@ -609,7 +609,7 @@ protected:
 
     T* m_raw;
 
-    template<bool x, bool y, ShouldWeakPointersBeMarkedStrongly z, typename U, typename V> friend struct CollectionBackingTraceTrait;
+    template<bool x, WTF::WeakHandlingFlag y, ShouldWeakPointersBeMarkedStrongly z, typename U, typename V> friend struct CollectionBackingTraceTrait;
     friend class Visitor;
 };
 
@@ -1042,6 +1042,12 @@ template<typename T> struct HashTraits<WebCore::WeakMember<T> > : SimpleClassHas
 
     static PeekOutType peek(const WebCore::WeakMember<T>& value) { return value; }
     static PassOutType passOut(const WebCore::WeakMember<T>& value) { return value; }
+    static bool shouldRemoveFromCollection(WebCore::Visitor* visitor, WebCore::WeakMember<T>& value) { return !visitor->isAlive(value); }
+    static void traceInCollection(WebCore::Visitor* visitor, WebCore::WeakMember<T>& weakMember, WebCore::ShouldWeakPointersBeMarkedStrongly strongify)
+    {
+        if (strongify == WebCore::WeakPointersActStrong)
+            visitor->trace(reinterpret_cast<WebCore::Member<T>&>(weakMember)); // Strongified visit.
+    }
 };
 
 template<typename T> struct PtrHash<WebCore::Member<T> > : PtrHash<T*> {
@@ -1088,11 +1094,6 @@ struct IsWeak<WebCore::WeakMember<T> > {
     static const bool value = true;
 };
 
-template<typename Table>
-struct IsWeak<WebCore::HeapHashTableBacking<Table> > {
-    static const bool value = Table::ValueTraits::isWeak;
-};
-
 template<typename T> inline T* getPtr(const WebCore::Member<T>& p)
 {
     return p.get();