Add SF side tunnel mode listener

This CL adds a TunnelModeStateReporter, which monitors if there are
any layers with a sideband stream in SurfaceFlinger. If any of the
layers have a sideband stream, it informs all the registered listeners
that tunnel mode is enabled. When no layers have a sideband stream, it
notifies the listeners that tunnel mode is disabled.

Bug: 171457637
Test: atest TunnelModeStateListenerTest
Test: atest TunnelModeStateReporterTest
Change-Id: Ie54b34dbd9b6253d7142e9b0f690c8469374604d
diff --git a/services/surfaceflinger/tests/unittests/Android.bp b/services/surfaceflinger/tests/unittests/Android.bp
index b33434e..1b25a36 100644
--- a/services/surfaceflinger/tests/unittests/Android.bp
+++ b/services/surfaceflinger/tests/unittests/Android.bp
@@ -86,6 +86,7 @@
         "TransactionApplicationTest.cpp",
         "TransactionFrameTracerTest.cpp",
         "TransactionSurfaceFrameTest.cpp",
+        "TunnelModeEnabledReporterTest.cpp",
         "StrongTypingTest.cpp",
         "VSyncDispatchTimerQueueTest.cpp",
         "VSyncDispatchRealtimeTest.cpp",