Add Shell permission for CTS test.

Add Shell permission for new CTS tests to test the multi-display
functionality in WallpaperService/WallpaperManagerService.

Bug: 123707989
Test: atest WallpaperManagerMultiDisplayTests
Test: atest ActivityManagerMultiDisplayTests

Change-Id: Id97db050a0b9d1940c2dfaa793fbe526df578105
diff --git a/test-mock/api/test-current.txt b/test-mock/api/test-current.txt
index 6765316..a87e2f5 100644
--- a/test-mock/api/test-current.txt
+++ b/test-mock/api/test-current.txt
@@ -3,6 +3,7 @@
 
   public class MockContext extends android.content.Context {
     method public android.view.Display getDisplay();
+    method public int getDisplayId();
   }
 
   @Deprecated public class MockPackageManager extends android.content.pm.PackageManager {