Oilpan: have LifetimeNotifier<T> track its observers weakly.

Source/bindings/core/v8/ScriptPromiseResolver.cpp

Index: Source/bindings/core/v8/ScriptPromiseResolver.cpp
diff --git a/Source/bindings/core/v8/ScriptPromiseResolver.cpp b/Source/bindings/core/v8/ScriptPromiseResolver.cpp
index d3950a4cf79cb8910b65a2a7be64473ed66619bb..1262870f2cc5ba0c4e03f1dae01aad038f9cf833 100644
--- a/Source/bindings/core/v8/ScriptPromiseResolver.cpp
+++ b/Source/bindings/core/v8/ScriptPromiseResolver.cpp
@@ -26,14 +26,6 @@ ScriptPromiseResolver::ScriptPromiseResolver(ScriptState* scriptState)
         m_resolver.clear();
     }
 #if ENABLE(OILPAN) && ENABLE(ASSERT)
-    // A prefinalizer has already been registered (as a LifecycleObserver);
-    // remove it and register a combined one, as the infrastructure doesn't
-    // support multiple prefinalizers for an object.
-    //
-    // FIXME: Oilpan: remove LifecycleObserver's need for a prefinalizer,
-    // and as a consequence, this unregistration step. If the former is
-    // independently removed, the unregisterPreFinalizer() call will assert.
-    ThreadState::current()->unregisterPreFinalizer(*static_cast<LifecycleObserver*>(this));
     ThreadState::current()->registerPreFinalizer(*this);
 #endif
 }