SF: Adding Idle Timer, to detect when devices are idle.

If SF has not received request for the next vsync in 30ms, the device is
considered idle.

The timeout ms can be set via setprop flag: debug.sf.set_idle_timer_ms

see go/surface-flinger-scheduler for more info.

Test: Adding tests for new class.
Bug: 113612090
Change-Id: I5dae075012f3fef9bb8ed48121367c80dff39de0
diff --git a/services/surfaceflinger/Android.bp b/services/surfaceflinger/Android.bp
index 22e4d1e..0106b25 100644
--- a/services/surfaceflinger/Android.bp
+++ b/services/surfaceflinger/Android.bp
@@ -139,6 +139,7 @@
         "Scheduler/DispSyncSource.cpp",
         "Scheduler/EventControlThread.cpp",
         "Scheduler/EventThread.cpp",
+        "Scheduler/IdleTimer.cpp",
         "Scheduler/LayerHistory.cpp",
         "Scheduler/MessageQueue.cpp",
         "Scheduler/Scheduler.cpp",