Reset cached light sensor values when toggling auto-brightness mode

Now the screen brightness will readjust to ambient lighting when toggling
auto-brightness on and off in Settings or the Power Widget.

Bug: 5486091

Change-Id: Ic98939fe1c59cb8def0f84266e48ca00329d6b30
Signed-off-by: Mike Lockwood <lockwood@android.com>

services/java/com/android/server/PowerManagerService.java

@@ -3043,6 +3043,11 @@ public class PowerManagerService extends IPowerManager.Stub
         }
         if (mSensorManager != null && mLightSensorEnabled != enable) {
             mLightSensorEnabled = enable;
+            // clear previous values so we will adjust to current brightness when
+            // auto-brightness is reenabled
+            mHighestLightSensorValue = -1;
+            mLightSensorValue = -1;
+
             // clear calling identity so sensor manager battery stats are accurate
             long identity = Binder.clearCallingIdentity();
             try {