SF: Flag guard setFrameRate() API

- LayerHistory is now always created
- Do not use LayerHistory when content detection flag is turned off.

Bug: 148428554
Test: atest CtsGraphicsTestCases:SetFrameRateTest
Test: Play YouTube video. When content detection flag is off,
      display runs at 90, otherwise at 60.
Test: adb shell /data/.../libsurfaceflinger_unittest
Change-Id: Iab8b79e16a5257c770d9ddd204cfe26d22de83b6
diff --git a/services/surfaceflinger/sysprop/SurfaceFlingerProperties.sysprop b/services/surfaceflinger/sysprop/SurfaceFlingerProperties.sysprop
index 71f8d6a..b19eae6 100644
--- a/services/surfaceflinger/sysprop/SurfaceFlingerProperties.sysprop
+++ b/services/surfaceflinger/sysprop/SurfaceFlingerProperties.sysprop
@@ -393,3 +393,13 @@
     access: Readonly
     prop_name: "ro.surface_flinger.supports_background_blur"
 }
+
+# Indicates whether Scheduler should use frame rate API when adjusting the
+# display refresh rate.
+prop {
+    api_name: "use_frame_rate_api"
+    type: Boolean
+    scope: Public
+    access: Readonly
+    prop_name: "ro.surface_flinger.use_frame_rate_api"
+}