shill: enable background scanning for wifi

When connecting to a WiFi service, supply wpa_supplicant with background
scan configuration parameters. Also, allow bgscan parameters to be
configured via RPC.

Collateral change: added NOTIMPLEMENTED log messages for ClearProperty
methods on {Device,IPConfig,Service}DBusAdaptor

BUG=chromium-os:24309
TEST=unit tests, WiFiRoaming.003SSIDMultiSwitchBack

Change-Id: I3289684bcae58a01be61d2341fd6a1099c1c7f6f
Reviewed-on: https://gerrit.chromium.org/gerrit/13844
Tested-by: mukesh agrawal <quiche@chromium.org>
Reviewed-by: Thieu Le <thieule@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Ready: mukesh agrawal <quiche@chromium.org>
diff --git a/property_store.cc b/property_store.cc
index 2b6fbe7..9b8757b 100644
--- a/property_store.cc
+++ b/property_store.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
+// Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -291,6 +291,11 @@
   bool_properties_[name] = accessor;
 }
 
+void PropertyStore::RegisterDerivedInt32(const std::string &name,
+                                         const Int32Accessor &accessor) {
+  int32_properties_[name] = accessor;
+}
+
 void PropertyStore::RegisterDerivedString(const std::string &name,
                                           const StringAccessor &accessor) {
   string_properties_[name] = accessor;