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/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index e8c7a55..1a4d316 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -228,6 +228,7 @@
 ui::PixelFormat SurfaceFlinger::defaultCompositionPixelFormat = ui::PixelFormat::RGBA_8888;
 Dataspace SurfaceFlinger::wideColorGamutCompositionDataspace = Dataspace::V0_SRGB;
 ui::PixelFormat SurfaceFlinger::wideColorGamutCompositionPixelFormat = ui::PixelFormat::RGBA_8888;
+bool SurfaceFlinger::useFrameRateApi;
 
 std::string getHwcServiceName() {
     char value[PROPERTY_VALUE_MAX] = {};
@@ -387,6 +388,8 @@
         // for production purposes later on.
         setenv("TREBLE_TESTING_OVERRIDE", "true", true);
     }
+
+    useFrameRateApi = use_frame_rate_api(true);
 }
 
 void SurfaceFlinger::onFirstRef()