Fix adb shell command for screen_brightness

This was caused by ag/10665448 removing BrightnessSynchronizer from
DisplayPowerController.

Bug: 153744973

Test: atest android.cts.statsd.atom.UidAtomTests#testScreenBrightness
Manual, check brightness changes accordingly:
adb shell settings put system screen_brightness_float 0.9
adb shell settings put system screen_brightness 2

Change-Id: I86c80ae1aa1d34d9221a09da11a48f9845506bea

services/core/java/com/android/server/display/DisplayPowerController.java

@@ -389,6 +389,10 @@ final class DisplayPowerController implements AutomaticBrightnessController.Call
     private ObjectAnimator mColorFadeOffAnimator;
     private RampAnimator<DisplayPowerState> mScreenBrightnessRampAnimator;
 
+    // The brightness synchronizer to allow changes in the int brightness value to be reflected in
+    // the float brightness value and vice versa.
+    @Nullable
+    private final BrightnessSynchronizer mBrightnessSynchronizer;
 
     /**
      * Creates the display power controller.
@@ -405,6 +409,7 @@ final class DisplayPowerController implements AutomaticBrightnessController.Call
         mWindowManagerPolicy = LocalServices.getService(WindowManagerPolicy.class);
         mBlanker = blanker;
         mContext = context;
+        mBrightnessSynchronizer = new BrightnessSynchronizer(context);
         mDisplayDevice = displayDevice;
 
         PowerManager pm =  context.getSystemService(PowerManager.class);