[Device Service] Decouple NFC implementation from //content

device/nfc/public/java/src/org/chromium/device/nfc/NfcDelegate.java

Index: device/nfc/public/java/src/org/chromium/device/nfc/NfcDelegate.java
diff --git a/device/nfc/public/java/src/org/chromium/device/nfc/NfcDelegate.java b/device/nfc/public/java/src/org/chromium/device/nfc/NfcDelegate.java
new file mode 100644
index 0000000000000000000000000000000000000000..95ba2ee27680eef11378c2862cb46816fe9d46e6
--- /dev/null
+++ b/device/nfc/public/java/src/org/chromium/device/nfc/NfcDelegate.java
@@ -0,0 +1,29 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.device.nfc;
+
+import android.app.Activity;
+
+import org.chromium.base.Callback;
+
+/**
+ * Interface that allows the NFC implementation to access the Activity
+ * associated with a given client. |hostId| is the same ID passed in
+ * NFCProvider::GetNFCForHost().
+ */
+public interface NfcDelegate {
+    /**
+     * Calls |callback| with the Activity associated with |hostId|, and
+     * subsequently calls |callback| again whenever the Activity associated
+     * with |hostId| changes.
+     */
+    void trackActivityForHost(int hostId, Callback<Activity> callback);
+
+    /**
+     * Called when the NFC implementation no longer needs to track the
+     * Activity associated with |hostId|.
+     */
+    void stopTrackingActivityForHost(int hostId);
+}