Use distinct value for BAL_BLOCK

Instead of logging 0 which can be misinterpreted as "missing data" in
protos, use a distinct value defined in the proto enum.

Test: atest BackgroundActivityStartController*Test
Flag: com.android.window.flags.bal_improved_metrics
Bug: 339245692
Change-Id: I6126990f9668e35fe876ceae3cdf94e8f407bcad
diff --git a/services/core/java/com/android/server/wm/BackgroundActivityStartController.java b/services/core/java/com/android/server/wm/BackgroundActivityStartController.java
index 3f4bda7..e94b857 100644
--- a/services/core/java/com/android/server/wm/BackgroundActivityStartController.java
+++ b/services/core/java/com/android/server/wm/BackgroundActivityStartController.java
@@ -142,7 +142,7 @@
     })
     public @interface BalCode {}
 
-    static final int BAL_BLOCK = 0;
+    static final int BAL_BLOCK = FrameworkStatsLog.BAL_ALLOWED__ALLOWED_REASON__BAL_BLOCKED;
 
     static final int BAL_ALLOW_DEFAULT =
             FrameworkStatsLog.BAL_ALLOWED__ALLOWED_REASON__BAL_ALLOW_DEFAULT;