Use SoftAp API to get number of connected device

Create unit test because robolectric doesn't have the new API

Bug: 68058038
Test: SettingsUnitTest

Change-Id: I9fa27d51c4d270b2fb92db7dfc3955e33d4a3f4a

src/com/android/settings/wifi/tether/WifiTetherSoftApManager.java

@@ -0,0 +1,47 @@
+package com.android.settings.wifi.tether;
+
+import android.net.wifi.WifiManager;
+import android.os.Handler;
+
+/**
+ * Wrapper for {@link android.net.wifi.WifiManager.SoftApCallback} to pass the robo test
+ */
+public class WifiTetherSoftApManager {
+
+    private WifiManager mWifiManager;
+    private WifiTetherSoftApCallback mWifiTetherSoftApCallback;
+
+    private WifiManager.SoftApCallback mSoftApCallback = new WifiManager.SoftApCallback() {
+        @Override
+        public void onStateChanged(int state, int failureReason) {
+            mWifiTetherSoftApCallback.onStateChanged(state, failureReason);
+        }
+
+        @Override
+        public void onNumClientsChanged(int numClients) {
+            mWifiTetherSoftApCallback.onNumClientsChanged(numClients);
+        }
+    };
+    private Handler mHandler;
+
+    WifiTetherSoftApManager(WifiManager wifiManager,
+            WifiTetherSoftApCallback wifiTetherSoftApCallback) {
+        mWifiManager = wifiManager;
+        mWifiTetherSoftApCallback = wifiTetherSoftApCallback;
+        mHandler = new Handler();
+    }
+
+    public void registerSoftApCallback() {
+        mWifiManager.registerSoftApCallback(mSoftApCallback, mHandler);
+    }
+
+    public void unRegisterSoftApCallback() {
+        mWifiManager.unregisterSoftApCallback(mSoftApCallback);
+    }
+
+    public interface WifiTetherSoftApCallback {
+        void onStateChanged(int state, int failureReason);
+
+        void onNumClientsChanged(int numClients);
+    }
+}