Add VPN settings classes to Settings app.

PATCH SET 2:
+ Add import com.android.settings.R

PATCH SET 3:
+ Remove @Override interface methods to be compilable by Java 1.5.

PATCH SET 4:
+ Add import android.net.vpn.VpnManager

PATCH SET 5:
+ Add license headers.

PATCH SET 6:
+ Remove Constant.java and move the constants to VpnSettings.
+ Make AuthenticationActor implement DialogInterface's handlers.
+ Remove trailing spaces.

PATCH SET 7:
+ Remove default username.

src/com/android/settings/vpn/VpnProfileEditor.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright (C) 2007 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.vpn;
+
+import android.content.Context;
+import android.net.vpn.VpnProfile;
+import android.preference.PreferenceGroup;
+
+/**
+ * The interface to set up preferences for editing a {@link VpnProfile}.
+ */
+public interface VpnProfileEditor {
+    VpnProfile getProfile();
+
+    /**
+     * Adds the preferences to the panel.
+     */
+    void loadPreferencesTo(PreferenceGroup subpanel);
+
+    /**
+     * Validates the inputs in the preferences.
+     *
+     * @return an error message that is ready to be displayed in a dialog; or
+     *      null if all the inputs are valid
+     */
+    String validate(Context c);
+}