Add TetheredInterface{Request, Callback} interface

Define interfaces that match the signature of the existing
EthernetManager.TetheredInterfaceRequest and TetheredInterfaceCallback
classes and make EthernetManager.TetheredInterfaceRequest and
TetheredInterfaceCallback implement/subinterface these interfaces. The
new bluetooth API could also implement these interfaces to make API surface
consistent.

Test: TH would test the existing tests that use the subclass.
Bug: 190438212
Change-Id: I093972c111cb1d921076782492716d5a046be8fc

Tethering/common/TetheringLib/src/android/net/TetheringManager.java

@@ -22,6 +22,7 @@ import android.annotation.IntDef;
 import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.annotation.RequiresPermission;
+import android.annotation.SuppressLint;
 import android.annotation.SystemApi;
 import android.content.Context;
 import android.os.Bundle;
@@ -444,6 +445,44 @@ public class TetheringManager {
         }
     }
 
+    /**
+     * A request for a tethered interface.
+     *
+     * There are two reasons why this doesn't implement CLoseable:
+     * 1. To consistency with the existing EthernetManager.TetheredInterfaceRequest, which is
+     * already released.
+     * 2. This is not synchronous, so it's not useful to use try-with-resources.
+     *
+     * {@hide}
+     */
+    @SystemApi(client = MODULE_LIBRARIES)
+    @SuppressLint("NotCloseable")
+    public interface TetheredInterfaceRequest {
+        /**
+         * Release the request to tear down tethered interface.
+         */
+        void release();
+    }
+
+    /**
+     * Callback for requestTetheredInterface.
+     *
+     * {@hide}
+     */
+    @SystemApi(client = MODULE_LIBRARIES)
+    public interface TetheredInterfaceCallback {
+        /**
+         * Called when the tethered interface is available.
+         * @param iface The name of the interface.
+         */
+        void onAvailable(@NonNull String iface);
+
+        /**
+         * Called when the tethered interface is now unavailable.
+         */
+        void onUnavailable();
+    }
+
     private static class TetheringCallbackInternal extends ITetheringEventCallback.Stub {
         private volatile int mError = TETHER_ERROR_NO_ERROR;
         private final ConditionVariable mWaitForCallback = new ConditionVariable();