sync: add WIFI_CREDENTIALS protobuf, ModelType, and preference

sync/protocol/wifi_credential_specifics.proto

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+// Sync protocol datatype extension for WiFi credentials.
+
+// Update proto_{value,enum}_conversions{.h,.cc,_unittest.cc} if you change
+// any fields in this file.
+
+syntax = "proto2";
+
+option optimize_for = LITE_RUNTIME;
+option retain_unknown_fields = true;
+
+package sync_pb;
+
+// Properties of WiFi credential objects.
+message WifiCredentialSpecifics {
+  optional bytes ssid = 1;  // Not necessarily UTF-8. May contain NUL.
+
+  enum SecurityClass {
+    SECURITY_CLASS_INVALID = 0;
+    SECURITY_CLASS_NONE = 1;
+    SECURITY_CLASS_WEP = 2;
+    SECURITY_CLASS_PSK = 3;  // WPA-PSK or RSN-PSK
+    // 802.1X is omittted, as we do not support syncing 802.1X
+    // credentials.
+  }
+  optional SecurityClass security_class = 2;
+
+  // Network passphrase.
+  //
+  // For SECURITY_CLASS_NONE, the passphrase should be ignored.
+  //
+  // For SECURITY_CLASS_WEP, the passphrase should have one of the
+  // following formats:
+  // - WEP-40:
+  //   - 5 character ASCII string. Each character maps one byte of the key.
+  //   - 10 character hex string. The string maps to the WEP key by simple
+  //     hex decoding.
+  // - WEP-104:
+  //   - 13 character ASCII string. Each character maps one byte of the key.
+  //   - 26 character hex string. The string maps to the WEP key by simple
+  //     hex decoding.
+  //
+  // For SECURITY_CLASS_PSK, the passphrase should have one of the
+  // following two formats:
+  // - An 8-63 character ASCII string. The string maps to the
+  //   WPA/WPA-2 PSK as per IEEE 802.11i.
+  // - A 64 character hex string. The string maps to the PSK per
+  //   simple hex decoding.
+  //
+  // Note that, although the passphrase "should" contain only ASCII
+  // characters, we represent |passphrase| as |bytes| rather than
+  // |string|. This is to accomodate networks that use non-ASCII
+  // passphrases.
+  optional bytes passphrase = 3;
+}