add subscribeOn(computation()) to the ObserveOn perf methods

Author: davidmoten

src/perf/java/rx/operators/OperatorObserveOnPerf.java

@@ -49,21 +49,21 @@ public int getSize() {
     @Benchmark
     public void observeOnComputation(Input input) throws InterruptedException {
         LatchedObserver<Integer> o = input.newLatchedObserver();
-        input.observable.observeOn(Schedulers.computation()).subscribe(o);
+        input.observable.subscribeOn(Schedulers.computation()).observeOn(Schedulers.computation()).subscribe(o);
         o.latch.await();
     }
 
     @Benchmark
     public void observeOnNewThread(Input input) throws InterruptedException {
         LatchedObserver<Integer> o = input.newLatchedObserver();
-        input.observable.observeOn(Schedulers.newThread()).subscribe(o);
+        input.observable.subscribeOn(Schedulers.computation()).observeOn(Schedulers.newThread()).subscribe(o);
         o.latch.await();
     }
 
     @Benchmark
     public void observeOnImmediate(Input input) throws InterruptedException {
         LatchedObserver<Integer> o = input.newLatchedObserver();
-        input.observable.observeOn(Schedulers.immediate()).subscribe(o);
+        input.observable.subscribeOn(Schedulers.computation()).observeOn(Schedulers.immediate()).subscribe(o);
         o.latch.await();
     }