Add Telecom debug setting for enabling enhanced call blocking.

This feature is only available for certain carriers at the current time.
To facilitate test team productivity, adding a system setting which can
be accessed from the Telecom debug menu to enable this functionality.

Test: Manual
Bug: 28189985
Change-Id: I4c812cecd2832a722e5dc73b7c719a9e0594064d
diff --git a/core/tests/coretests/src/android/provider/SettingsBackupTest.java b/core/tests/coretests/src/android/provider/SettingsBackupTest.java
index 757a70c..50fa48f 100644
--- a/core/tests/coretests/src/android/provider/SettingsBackupTest.java
+++ b/core/tests/coretests/src/android/provider/SettingsBackupTest.java
@@ -64,6 +64,7 @@
                     Settings.System.NOTIFICATION_LIGHT_PULSE, // candidate for backup?
                     Settings.System.NOTIFICATION_SOUND_CACHE, // internal cache
                     Settings.System.POINTER_LOCATION, // backup candidate?
+                    Settings.System.DEBUG_ENABLE_ENHANCED_CALL_BLOCKING, // used for testing only
                     Settings.System.RINGTONE_CACHE, // internal cache
                     Settings.System.SETUP_WIZARD_HAS_RUN, // Only used by SuW
                     Settings.System.SHOW_GTALK_SERVICE_STATUS, // candidate for backup?