Verify caller before auto granting slice permission

Currently SliceManagerService#checkSlicePermission does not verify the
caller's identity. This leads to a security vulnerability because
checkSlicePermission does more than checking the permission as opposed
to simply return a boolean value -- it additionally grants slice access
under a certain condition. A malicious app can spoof the calling package
to acquire slice access.

This CL verifies the caller before granting slice access.

Bug: 208232850
Test: manual
Change-Id: I2539c9ff5ea977c91bb58185c95280b4d533a520

services/core/java/com/android/server/slice/SliceManagerService.java

@@ -247,6 +247,8 @@ public class SliceManagerService extends ISliceManager.Stub {
         if (autoGrantPermissions != null && callingPkg != null) {
             // Need to own the Uri to call in with permissions to grant.
             enforceOwner(callingPkg, uri, userId);
+            // b/208232850: Needs to verify caller before granting slice access
+            verifyCaller(callingPkg);
             for (String perm : autoGrantPermissions) {
                 if (mContext.checkPermission(perm, pid, uid) == PERMISSION_GRANTED) {
                     int providerUser = ContentProvider.getUserIdFromUri(uri, userId);