Don't assert when ServiceWorker::from is passed an empty promise

Source/bindings/v8/ScriptPromise.cpp

Index: Source/bindings/v8/ScriptPromise.cpp
diff --git a/Source/bindings/v8/ScriptPromise.cpp b/Source/bindings/v8/ScriptPromise.cpp
index 11865ee4854c9fd76b572354a85ebfa60b06eca2..cdeeb0586de15f19c3555019e0ae9e7d00be498e 100644
--- a/Source/bindings/v8/ScriptPromise.cpp
+++ b/Source/bindings/v8/ScriptPromise.cpp
@@ -67,13 +67,13 @@ ScriptPromise::ScriptPromise(ScriptState* scriptState, v8::Handle<v8::Value> val
 
 ScriptPromise ScriptPromise::then(PassOwnPtr<ScriptFunction> onFulfilled, PassOwnPtr<ScriptFunction> onRejected)
 {
+    v8::Local<v8::Function> v8OnFulfilled = ScriptFunction::adoptByGarbageCollector(onFulfilled);
+    v8::Local<v8::Function> v8OnRejected = ScriptFunction::adoptByGarbageCollector(onRejected);

[haraken, 2014/06/17 00:51:55]

Would you elaborate on this change? It seems a bit strange to me that just
adopting ScriptFunctions addresses some issue. Also in a case where a
ScriptPromise is empty, I wonder why we need to adopt ScriptFunctions.

[falken, 2014/06/17 01:07:51]

The destructor of PassOwnPtr deletes the ScriptFunction, but ScriptFunction
inherits V8GarbageCollected whose dtor will ASSERT that m_handle was set. AFAICT
the way to set m_handle is to call adoptbyGarbageCollector.

So I think the caller expects ScriptPromise::then to always adopt the args.

[haraken, 2014/06/17 01:15:25]

Thanks for the details; that ASSERT doesn't make much sense to me. Can we change
the ASSERT to something like ASSERT(alreadyAdopted || m_handle) ?

+
     if (m_promise.isEmpty())
         return ScriptPromise();
 
     v8::Local<v8::Object> promise = m_promise.v8Value().As<v8::Object>();
-    v8::Local<v8::Function> v8OnFulfilled = ScriptFunction::adoptByGarbageCollector(onFulfilled);
-    v8::Local<v8::Function> v8OnRejected = ScriptFunction::adoptByGarbageCollector(onRejected);
-
     ASSERT(promise->IsPromise());
     // Return this Promise if no handlers are given.
     // In fact it is not the exact bahavior of Promise.prototype.then