shill: tighten up constness of PropertyStore

BUG=chromium-os:20543
TEST=unittest

Change-Id: Ifa86f82a883b3c3ec61ce10f8d82564b9a036b04
Reviewed-on: http://gerrit.chromium.org/gerrit/7901
Tested-by: mukesh agrawal <quiche@chromium.org>
Reviewed-by: Chris Masone <cmasone@chromium.org>
diff --git a/dhcp_config_unittest.cc b/dhcp_config_unittest.cc
index a8c7b8a..45c62fc 100644
--- a/dhcp_config_unittest.cc
+++ b/dhcp_config_unittest.cc
@@ -332,13 +332,13 @@
 }
 
 TEST_F(DHCPConfigTest, Dispatch) {
-  EXPECT_TRUE(DBusAdaptor::DispatchOnType(config_->store(),
+  EXPECT_TRUE(DBusAdaptor::DispatchOnType(config_->mutable_store(),
                                           flimflam::kMtuProperty,
                                           PropertyStoreTest::kInt32V,
                                           NULL));
   ::DBus::Error error;
   // Ensure that an attempt to write a R/O property returns InvalidArgs error.
-  EXPECT_FALSE(DBusAdaptor::DispatchOnType(config_->store(),
+  EXPECT_FALSE(DBusAdaptor::DispatchOnType(config_->mutable_store(),
                                            flimflam::kAddressProperty,
                                            PropertyStoreTest::kStringV,
                                            &error));