shill: Cellular: cleanup proxy interfaces

Remove dbus-c++ dependency from cellular proxy interfaces.

The changes include:
- Replace DBusPropertiesMap with KeyValueStore.
- Replace DBus::Path with std::string.
- Initialize proxies using service's well known name (service_name)
  instead of service owner's name (owner), since there can only
  be one owner per service and it is easier to use service_name with
  the new proxy setup.
- Replace DBus::Struct with std::tuple.

An upcoming CL will implement proxies using chromeos dbus, and integrate
them into ChromeosDBusControl.

BUG=chromium:517680
TEST=USE="chromeos_dbus asan clang" FEATURES=test emerge-$BOARD shill

Change-Id: I041369f69e7160a471efc8f90eef1d909df1a776
Reviewed-on: https://chromium-review.googlesource.com/293796
Commit-Ready: Zeping Qiu <zqiu@chromium.org>
Tested-by: Zeping Qiu <zqiu@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
diff --git a/cellular/mock_cellular.h b/cellular/mock_cellular.h
index 8ebe4ae..dfab615 100644
--- a/cellular/mock_cellular.h
+++ b/cellular/mock_cellular.h
@@ -21,16 +21,15 @@
                const std::string& address,
                int interface_index,
                Type type,
-               const std::string& owner,
                const std::string& service,
                const std::string& path);
   ~MockCellular() override;
 
   MOCK_METHOD1(Connect, void(Error* error));
   MOCK_METHOD2(Disconnect, void(Error* error, const char* reason));
-  MOCK_METHOD3(OnDBusPropertiesChanged, void(
+  MOCK_METHOD3(OnPropertiesChanged, void(
       const std::string& interface,
-      const DBusPropertiesMap& changed_properties,
+      const KeyValueStore& changed_properties,
       const std::vector<std::string>& invalidated_properties));
   MOCK_METHOD1(set_modem_state, void(ModemState state));
   MOCK_METHOD0(DestroyService, void());