Change TOP_TO_FGS_GRACE_DURATION to be DeviceConfig

It was still a global setting.

Bug: n/a
Test: Manual test using the following commands
- `dumpsys activity settings | grep -w top_to_fgs_grace_duration`
- `device_config put activity_manager top_to_fgs_grace_duration 5000`
- also adb reboot and make sure it's persisted

Change-Id: I5d058bc7a6845e4c154c5bacef5489b0be512d68

services/core/java/com/android/server/am/ActivityManagerConstants.java

@@ -513,7 +513,7 @@ final class ActivityManagerConstants extends ContentObserver {
 
     // Allow app just moving from TOP to FOREGROUND_SERVICE to stay in a higher adj value for
     // this long.
-    public long TOP_TO_FGS_GRACE_DURATION = DEFAULT_TOP_TO_FGS_GRACE_DURATION;
+    public volatile long TOP_TO_FGS_GRACE_DURATION = DEFAULT_TOP_TO_FGS_GRACE_DURATION;
 
     /**
      * Allow app just leaving TOP with an already running ALMOST_PERCEPTIBLE service to stay in
@@ -1142,6 +1142,8 @@ final class ActivityManagerConstants extends ContentObserver {
                             case KEY_LOW_SWAP_THRESHOLD_PERCENT:
                                 updateLowSwapThresholdPercent();
                                 break;
+                            case KEY_TOP_TO_FGS_GRACE_DURATION:
+                                updateTopToFgsGraceDuration();
                             default:
                                 break;
                         }
@@ -1359,8 +1361,6 @@ final class ActivityManagerConstants extends ContentObserver {
                     DEFAULT_PROCESS_START_ASYNC);
             MEMORY_INFO_THROTTLE_TIME = mParser.getLong(KEY_MEMORY_INFO_THROTTLE_TIME,
                     DEFAULT_MEMORY_INFO_THROTTLE_TIME);
-            TOP_TO_FGS_GRACE_DURATION = mParser.getDurationMillis(KEY_TOP_TO_FGS_GRACE_DURATION,
-                    DEFAULT_TOP_TO_FGS_GRACE_DURATION);
             TOP_TO_ALMOST_PERCEPTIBLE_GRACE_DURATION = mParser.getDurationMillis(
                     KEY_TOP_TO_ALMOST_PERCEPTIBLE_GRACE_DURATION,
                     DEFAULT_TOP_TO_ALMOST_PERCEPTIBLE_GRACE_DURATION);
@@ -1790,6 +1790,13 @@ final class ActivityManagerConstants extends ContentObserver {
                 DEFAULT_LOW_SWAP_THRESHOLD_PERCENT);
     }
 
+    private void updateTopToFgsGraceDuration() {
+        TOP_TO_FGS_GRACE_DURATION = DeviceConfig.getLong(
+                DeviceConfig.NAMESPACE_ACTIVITY_MANAGER,
+                KEY_TOP_TO_FGS_GRACE_DURATION,
+                DEFAULT_TOP_TO_FGS_GRACE_DURATION);
+    }
+
     private void updateMinAssocLogDuration() {
         MIN_ASSOC_LOG_DURATION = DeviceConfig.getLong(
                 DeviceConfig.NAMESPACE_ACTIVITY_MANAGER, KEY_MIN_ASSOC_LOG_DURATION,