Add missing isShellUser check

Bug: 160390416
Test: verified command still works from shell
Change-Id: I23bb06e00f1623e4f27c02d7eb2c0d273b40771b

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

@@ -3318,6 +3318,9 @@ public class ActivityManagerService extends IActivityManager.Stub
     @Override
     public boolean setProcessMemoryTrimLevel(String process, int userId, int level)
             throws RemoteException {
+        if (!isCallerShell()) {
+            throw new SecurityException("Only shell can call it");
+        }
         synchronized (this) {
             final ProcessRecord app = findProcessLocked(process, userId, "setProcessMemoryTrimLevel");
             if (app == null) {