Further cleanup around DBus interface classes.

* Removed the "Glib" part from the various DbusGlib class name and added
  "Wrapper" instead: only part of the methods here declared have
  anything to do with Glib; in essence, this is an interface containing
  wrappers for various DBus functions.

* Changed "Dbus" to "DBus", to comply with the rest of the world.

* Renamed the actual implementation "RealDBusWrapper" (instead of
  "Concrete").

* Separated out RealDBusWrapper into its own header file. Client code,
  which often only cares about the abstract class, does not need to pull
  it unless specifically requiring it.

* Cleaned up the includes in these headers.

Aside from all that, also renamed system_state.cc into
real_system_state.cc, as this is what this file contains.

BUG=None
TEST=Unit tests.

Change-Id: I015c407cbc159aba8b5925eb0e916ba604c829cd
Reviewed-on: https://chromium-review.googlesource.com/189373
Reviewed-by: Gilad Arnold <garnold@chromium.org>
Tested-by: Gilad Arnold <garnold@chromium.org>
Commit-Queue: Gilad Arnold <garnold@chromium.org>
diff --git a/mock_system_state.h b/mock_system_state.h
index e1dc4cc..a6e764f 100644
--- a/mock_system_state.h
+++ b/mock_system_state.h
@@ -10,7 +10,7 @@
 #include <metrics/metrics_library_mock.h>
 #include <policy/mock_device_policy.h>
 
-#include "update_engine/mock_dbus_interface.h"
+#include "update_engine/mock_dbus_wrapper.h"
 #include "update_engine/mock_gpio_handler.h"
 #include "update_engine/mock_p2p_manager.h"
 #include "update_engine/mock_payload_state.h"
@@ -141,7 +141,7 @@
   testing::NiceMock<MockPayloadState> mock_payload_state_;
   testing::NiceMock<MockGpioHandler>* mock_gpio_handler_;
   testing::NiceMock<UpdateAttempterMock>* mock_update_attempter_;
-  MockDbusGlib dbus_;
+  MockDBusWrapper dbus_;
 
   // These are the other object we own.
   Clock default_clock_;