Unnecessary dependency on Schedulers.trampoline() for non-time-based refcount operator

[mycallmax]

In the constructor of ObservableRefCount that takes ConnectableObservable<T> source as the argument, we set timeout to 0L. In that specific use case of ObservableRefCount, scheduler is never needed. It's only referenced in cancel() method but if timeout is 0, it won't be triggered at all because there is early return. I am wondering if we could avoid referencing Schedulers.trampoline() in that specific use case of ObservableRefCount to keep the dependency clear.

RxJava/src/main/java/io/reactivex/internal/operators/observable/ObservableRefCount.java

Lines 48 to 50 in 4a78cfc

	public ObservableRefCount(ConnectableObservable<T> source) {
	this(source, 1, 0L, TimeUnit.NANOSECONDS, Schedulers.trampoline());
	}

RxJava/src/main/java/io/reactivex/internal/operators/observable/ObservableRefCount.java

Lines 92 to 112 in 4a78cfc

	void cancel(RefConnection rc) {
	SequentialDisposable sd;
	synchronized (this) {
	if (connection == null || connection != rc) {
	return;
	}
	long c = rc.subscriberCount - 1;
	rc.subscriberCount = c;
	if (c != 0L || !rc.connected) {
	return;
	}
	if (timeout == 0L) {
	timeout(rc);
	return;
	}
	sd = new SequentialDisposable();
	rc.timer = sd;
	}
	sd.replace(scheduler.scheduleDirect(rc, timeout, unit));
	}

The reasons are the following:

1. In projects that don't depend on Schedulers class, if there is no reference to Schedulers, the whole Schedulers can be stripped out of the library after optimizations (e.g., proguard). With constructor that references Schedulers, the optimizer can't properly strip it out. In our quick test of our Android app, we were able to reduce the RxJava library size dependency from 51KB to 37KB (after optimization but before compression) by simply avoiding access to Schedulers in ObservableRefCount.
2. In terms of modularity, ObservableRefCount is just an operator so it by itself should probably not have dependency on what available pool of schedulers (Schedulers) there are. It should just know that there is some Scheduler that could be passed to ObservableRefCount when ObservableRefCount needs it.

[akarnokd]

Yes, it can be replaced by null. PR welcome.