Now SuspendableObject is being renamed to PausableObject by me :-)


> 1. SuspendableObject::GetExecutionContext should be called only from the main thread. Add DCHECK to check that the thread is the main thread.

We changed the direction a little bit: We found that ScriptPromiseResolver, that is a PausableObject, is used from not only the main thread but also worker thread. As we want to allow ScriptPromiseResolver to be accessed from any thread, it would be hard to keep the assumption that PausableObject is accessed only from the main thread.

Our current conclusion is to allow PausableObject to be accessed from any thread explicitly, and add DCHECK that the thread where GetExecution is called is same as one at the creation.