Add L2TP secret, L2TP/IPSec PSK support. Fix screen orientation.

* Changes
  + Add L2tpActor, L2tpEditor, L2tpIpsecPskActor.
  + Make L2tpIpsecEditor extend L2tpEditor.
  + Revise the code for saving username. Make
    VpnSettings.saveProfileToStorage() static.
  + Fix support for screen orientation change in both VpnSettings and
    VpnEditor.

  Patch Set 2:
  + Remove Util.isNullOrEmpty(). Use TextUtils.isEmpty() instead.
  + Remove unused imports. Wrap lines longer than 80 chars.

  Patch Set 3:
  + Fix all the strings according to UI feedback.
  + Remove all the added actor subclasses and move password to editor.
  + Remove VPN entry in Security & location.

  Patch Set 4:
  + Misc string fixes.

  Patch Set 5:
  + Add strings for credential storage settings.
  + Changed the error dialog icon.
  + Fix "Remember me" indentation in connect dialog.

  Patch Set 6:
  + resolve res/values/strings.xml

src/com/android/settings/vpn/L2tpEditor.java

@@ -0,0 +1,119 @@
+/*
+ * Copyright (C) 2009 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 com.android.settings.R;
+
+import android.content.Context;
+import android.net.vpn.L2tpProfile;
+import android.preference.CheckBoxPreference;
+import android.preference.EditTextPreference;
+import android.preference.Preference;
+import android.preference.PreferenceGroup;
+
+/**
+ * The class for editing {@link L2tpProfile}.
+ */
+class L2tpEditor extends VpnProfileEditor {
+    private CheckBoxPreference mSecret;
+    private EditTextPreference mSecretString;
+    private String mOriginalSecret;
+    private boolean mOriginalSecretEnabled;
+
+    public L2tpEditor(L2tpProfile p) {
+        super(p);
+    }
+
+    @Override
+    protected void loadExtraPreferencesTo(PreferenceGroup subpanel) {
+        Context c = subpanel.getContext();
+        subpanel.addPreference(createSecretPreference(c));
+        subpanel.addPreference(createSecretStringPreference(c));
+        mSecretString.setEnabled(mSecret.isChecked());
+
+        L2tpProfile profile = (L2tpProfile) getProfile();
+        mOriginalSecret = profile.getSecretString();
+        mOriginalSecretEnabled = profile.isSecretEnabled();
+    }
+
+    @Override
+    public String validate() {
+        String result = super.validate();
+        if (!mSecret.isChecked()) return result;
+
+        return ((result != null)
+                ? result
+                : validate(mSecretString, R.string.vpn_l2tp_secret));
+    }
+
+    @Override
+    public void saveSecrets(String originalProfileName) {
+        L2tpProfile profile = (L2tpProfile) getProfile();
+        // TODO: fill up the implementation after keystore is available
+    }
+
+    private Preference createSecretPreference(Context c) {
+        final L2tpProfile profile = (L2tpProfile) getProfile();
+        CheckBoxPreference secret = mSecret = new CheckBoxPreference(c);
+        boolean enabled = profile.isSecretEnabled();
+        setSecretTitle(secret, R.string.vpn_l2tp_secret, enabled);
+        secret.setChecked(enabled);
+        setSecretSummary(secret, enabled);
+        secret.setOnPreferenceChangeListener(
+                new Preference.OnPreferenceChangeListener() {
+                    public boolean onPreferenceChange(
+                            Preference pref, Object newValue) {
+                        boolean enabled = (Boolean) newValue;
+                        profile.setSecretEnabled(enabled);
+                        mSecretString.setEnabled(enabled);
+                        setSecretTitle(mSecret, R.string.vpn_l2tp_secret,
+                                enabled);
+                        setSecretSummary(mSecret, enabled);
+                        return true;
+                    }
+                });
+        return secret;
+    }
+
+    private Preference createSecretStringPreference(Context c) {
+        final L2tpProfile profile = (L2tpProfile) getProfile();
+        mSecretString = createSecretPreference(c,
+                R.string.vpn_l2tp_secret_string_title,
+                R.string.vpn_l2tp_secret,
+                profile.getSecretString(),
+                new Preference.OnPreferenceChangeListener() {
+                    public boolean onPreferenceChange(
+                            Preference pref, Object newValue) {
+                        profile.setSecretString((String) newValue);
+                        setSecretSummary(mSecretString,
+                                R.string.vpn_l2tp_secret,
+                                (String) newValue);
+                        return true;
+                    }
+                });
+        return mSecretString;
+    }
+
+    private void setSecretSummary(CheckBoxPreference secret, boolean enabled) {
+        Context c = secret.getContext();
+        String formatString = c.getString(enabled
+                ? R.string.vpn_is_enabled
+                : R.string.vpn_is_disabled);
+        secret.setSummary(String.format(
+                formatString, c.getString(R.string.vpn_l2tp_secret)));
+    }
+}