Bluetooth: Add pairing initiator extra

Remember if the pairing app was in the foreground.

Bug: 150156492
Test: pair two devices, unpair on one device, try to reconnect
Change-Id: I6f564857974146e0c18134648eb1e297e8afbc6f

core/java/android/bluetooth/BluetoothDevice.java

@@ -326,6 +326,26 @@ public final class BluetoothDevice implements Parcelable {
      */
     public static final String EXTRA_PAIRING_KEY = "android.bluetooth.device.extra.PAIRING_KEY";
 
+    /**
+     * Used as an int extra field in {@link #ACTION_PAIRING_REQUEST}
+     * intents as the value of passkey.
+     * @hide
+     */
+    public static final String EXTRA_PAIRING_INITIATOR =
+            "android.bluetooth.device.extra.PAIRING_INITIATOR";
+
+    /**
+     * Bluetooth pairing initiator, Foreground App
+     * @hide
+     */
+    public static final int EXTRA_PAIRING_INITIATOR_FOREGROUND = 1;
+
+    /**
+     * Bluetooth pairing initiator, Background
+     * @hide
+     */
+    public static final int EXTRA_PAIRING_INITIATOR_BACKGROUND = 2;
+
     /**
      * Bluetooth device type, Unknown
      */