Add toast error message for no WiFi on wireless debugging.

Show a toast to connect to a WiFi network when the user tries to
enable wireless debugging while not connected to any Wi-Fi network.

Bug: 150139061
Bug: 149843499

Test: make RunSettingsRoboTests ROBOTEST_FILTER=WirelessDebuggingPreferenceControllerTest
Test: make RunSettingsRoboTests ROBOTEST_FILTER=WirelessDebuggingEnablerTest

Change-Id: I389f5fddc874f60e8156ecf6ef2f1c6eddc1d7a5
Exempt-From-Owner-Approval: LGTM

src/com/android/settings/development/WirelessDebuggingEnabler.java

@@ -24,7 +24,9 @@ import android.os.Handler;
 import android.os.Looper;
 import android.provider.Settings;
 import android.util.Log;
+import android.widget.Toast;
 
+import com.android.settings.R;
 import com.android.settings.widget.SwitchWidgetController;
 import com.android.settingslib.core.lifecycle.Lifecycle;
 import com.android.settingslib.core.lifecycle.LifecycleObserver;
@@ -121,6 +123,15 @@ public class WirelessDebuggingEnabler implements SwitchWidgetController.OnSwitch
 
     @Override
     public boolean onSwitchToggled(boolean isChecked) {
+        if (isChecked && !WirelessDebuggingPreferenceController.isWifiConnected(mContext)) {
+            // No connected Wi-Fi network. Reset the switch to off.
+            Toast.makeText(
+                    mContext, R.string.adb_wireless_no_network_msg, Toast.LENGTH_LONG)
+                    .show();
+            mSwitchWidget.setChecked(false);
+            return false;
+        }
+
         writeAdbWifiSetting(isChecked);
         return true;
     }