SF: Adding testable Scheduler and updating tests.

This follows ag/6337080 for clearity

Test: updating tests.
Bug: 123998711
Change-Id: I8999b3a1f002a9f5fb705e7de61294e9bc094298
diff --git a/services/surfaceflinger/Scheduler/Scheduler.h b/services/surfaceflinger/Scheduler/Scheduler.h
index 10ffc7a..7b5278c 100644
--- a/services/surfaceflinger/Scheduler/Scheduler.h
+++ b/services/surfaceflinger/Scheduler/Scheduler.h
@@ -144,6 +144,8 @@
             impl::EventThread::InterceptVSyncsCallback interceptCallback);
 
 private:
+    friend class TestableScheduler;
+
     // Creates a connection on the given EventThread and forwards the given callbacks.
     sp<EventThreadConnection> createConnectionInternal(EventThread*, ResyncCallback&&);