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/update_attempter_mock.h b/update_attempter_mock.h
index 693cc57..5b57dbc 100644
--- a/update_attempter_mock.h
+++ b/update_attempter_mock.h
@@ -7,7 +7,7 @@
 
 #include <gmock/gmock.h>
 
-#include "update_engine/mock_dbus_interface.h"
+#include "update_engine/mock_dbus_wrapper.h"
 #include "update_engine/mock_system_state.h"
 #include "update_engine/update_attempter.h"
 
@@ -18,7 +18,7 @@
 class UpdateAttempterMock : public UpdateAttempter {
  public:
   explicit UpdateAttempterMock(MockSystemState* mock_system_state,
-                               MockDbusGlib* dbus)
+                               MockDBusWrapper* dbus)
       : UpdateAttempter(mock_system_state, dbus) {}
 
   MOCK_METHOD5(Update, void(const std::string& app_version,