Exposing TelephonyManager.isIccLockEnabled as a system API.

This was recently removed as part of un-exposing telephony
mainline related APIs (b/146983487), but being added back in R as GMSCore
already uses it (b/151742706).

Test: TH
Bug: 151742706
Bug: 146983487
Change-Id: If4e8e87c7dfbb261ee3abfec2a4774980c24d0c2
diff --git a/telephony/api/system-current.txt b/telephony/api/system-current.txt
index 9d1fa37..fe48401 100644
--- a/telephony/api/system-current.txt
+++ b/telephony/api/system-current.txt
@@ -806,6 +806,7 @@
     method public boolean isDataConnectivityPossible();
     method @RequiresPermission(android.Manifest.permission.READ_PRIVILEGED_PHONE_STATE) public boolean isDataEnabledForApn(int);
     method @RequiresPermission(android.Manifest.permission.READ_PRIVILEGED_PHONE_STATE) public boolean isEmergencyAssistanceEnabled();
+    method @RequiresPermission(android.Manifest.permission.READ_PRIVILEGED_PHONE_STATE) @WorkerThread public boolean isIccLockEnabled();
     method @Deprecated @RequiresPermission(anyOf={android.Manifest.permission.READ_PRIVILEGED_PHONE_STATE, android.Manifest.permission.READ_PHONE_STATE}) public boolean isIdle();
     method @RequiresPermission(android.Manifest.permission.READ_PRIVILEGED_PHONE_STATE) public boolean isInEmergencySmsMode();
     method @RequiresPermission(android.Manifest.permission.READ_PRIVILEGED_PHONE_STATE) public boolean isLteCdmaEvdoGsmWcdmaEnabled();