Make some NFC APIs @systemAPI.

Change-Id: I12e292563a517211e4fae7a1f64021758f396d1a
diff --git a/core/java/android/nfc/NfcAdapter.java b/core/java/android/nfc/NfcAdapter.java
index b0397d5..ad785ed 100644
--- a/core/java/android/nfc/NfcAdapter.java
+++ b/core/java/android/nfc/NfcAdapter.java
@@ -20,6 +20,7 @@
 
 import android.annotation.SdkConstant;
 import android.annotation.SdkConstant.SdkConstantType;
+import android.annotation.SystemApi;
 import android.app.Activity;
 import android.app.ActivityThread;
 import android.app.OnActivityPausedListener;
@@ -261,6 +262,7 @@
     public static final String EXTRA_READER_PRESENCE_CHECK_DELAY = "presence";
 
     /** @hide */
+    @SystemApi
     public static final int FLAG_NDEF_PUSH_NO_CONFIRM = 0x1;
 
     /** @hide */
@@ -652,6 +654,7 @@
      *
      * @hide
      */
+    @SystemApi
     public boolean enable() {
         try {
             return sService.enable();
@@ -679,7 +682,7 @@
      *
      * @hide
      */
-
+    @SystemApi
     public boolean disable() {
         try {
             return sService.disable(true);
@@ -932,6 +935,7 @@
     /**
      * @hide
      */
+    @SystemApi
     public void setNdefPushMessage(NdefMessage message, Activity activity, int flags) {
         if (activity == null) {
             throw new NullPointerException("activity cannot be null");
@@ -1359,6 +1363,7 @@
      * <p>This API is for the Settings application.
      * @hide
      */
+    @SystemApi
     public boolean enableNdefPush() {
         try {
             return sService.enableNdefPush();
@@ -1373,6 +1378,7 @@
      * <p>This API is for the Settings application.
      * @hide
      */
+    @SystemApi
     public boolean disableNdefPush() {
         try {
             return sService.disableNdefPush();