DO NOT MERGE: Fix ActivityManager#killBackgroundProcesses permissions

In the pevious CL, we incorrectly added the permission check in the
killBackgroundProcessesExcept. Now fix this issue.

Bug: 239423414
Bug: 223376078
Test: atest CtsAppTestCases:ActivityManagerTest
Merged-In: I35d20539ffac055a6d61260445620f45584bd9c5
Merged-In: Ieed6af77da1bc31cfecc5272b9f97971db7ae7b2
Merged-In: I8b8a427ee87339cc038e53adc0912283b05d2cfc
Change-Id: I9471a77188ee63ec32cd0c81569193e4ccad885b

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

@@ -3690,6 +3690,22 @@ public class ActivityManagerService extends IActivityManager.Stub
             throw new SecurityException(msg);
         }
+        final int callingUid = Binder.getCallingUid();
+        final int callingPid = Binder.getCallingPid();
+
+        ProcessRecord proc;
+        synchronized (mPidsSelfLocked) {
+            proc = mPidsSelfLocked.get(callingPid);
+        }
+        if (callingUid >= FIRST_APPLICATION_UID
+                && (proc == null || !proc.info.isSystemApp())) {
+            final String msg = "Permission Denial: killAllBackgroundProcesses() from pid="
+                    + callingPid + ", uid=" + callingUid + " is not allowed";
+            Slog.w(TAG, msg);
+            // Silently return to avoid existing apps from crashing.
+            return;
+        }
+
         final long callingId = Binder.clearCallingIdentity();
         try {
             synchronized (this) {
@@ -3730,22 +3746,6 @@ public class ActivityManagerService extends IActivityManager.Stub
             throw new SecurityException(msg);
         }
-        final int callingUid = Binder.getCallingUid();
-        final int callingPid = Binder.getCallingPid();
-
-        ProcessRecord proc;
-        synchronized (mPidsSelfLocked) {
-            proc = mPidsSelfLocked.get(callingPid);
-        }
-        if (callingUid >= FIRST_APPLICATION_UID
-                && (proc == null || !proc.info.isSystemApp())) {
-            final String msg = "Permission Denial: killAllBackgroundProcesses() from pid="
-                    + callingPid + ", uid=" + callingUid + " is not allowed";
-            Slog.w(TAG, msg);
-            // Silently return to avoid existing apps from crashing.
-            return;
-        }
-
         final long callingId = Binder.clearCallingIdentity();
         try {
             synchronized (this) {