SF: Add unit test for mode switching

Test: atest DisplayModeSwitchingTest
Bug: 190982486

Change-Id: Ie12ab8de5d93b8a3adbb818bdda9003f4c6bbed7
diff --git a/services/surfaceflinger/tests/unittests/Android.bp b/services/surfaceflinger/tests/unittests/Android.bp
index 3dc6d8b..af635f9 100644
--- a/services/surfaceflinger/tests/unittests/Android.bp
+++ b/services/surfaceflinger/tests/unittests/Android.bp
@@ -71,6 +71,7 @@
         "MessageQueueTest.cpp",
         "SurfaceFlinger_CreateDisplayTest.cpp",
         "SurfaceFlinger_DestroyDisplayTest.cpp",
+        "SurfaceFlinger_DisplayModeSwitching.cpp",
         "SurfaceFlinger_DisplayTransactionCommitTest.cpp",
         "SurfaceFlinger_GetDisplayNativePrimariesTest.cpp",
         "SurfaceFlinger_HotplugTest.cpp",