update_engine: Move ConnectionManager to an abstract Interface.

MockConnectionManager required to use one of ConnectionManager
constructors passing pointers that won't be use by the mock. This
patch moves the interface to its own ConnectionManagerInterface class.

BUG=None
TEST=unittests still pass.

Change-Id: I9ed09daf8e4256304be7dab30cfbe751901dc24b
Reviewed-on: https://chromium-review.googlesource.com/290120
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>
Trybot-Ready: Alex Deymo <deymo@chromium.org>
Tested-by: Alex Deymo <deymo@chromium.org>
diff --git a/payload_state.cc b/payload_state.cc
index ed7b775..a15d68b 100644
--- a/payload_state.cc
+++ b/payload_state.cc
@@ -10,7 +10,6 @@
 #include <base/logging.h>
 #include <base/strings/string_util.h>
 #include <base/strings/stringprintf.h>
-#include <base/format_macros.h>
 #include <policy/device_policy.h>
 
 #include "update_engine/clock.h"
@@ -176,7 +175,8 @@
   NetworkConnectionType network_connection_type;
   NetworkTethering tethering;
   RealDBusWrapper dbus_iface;
-  ConnectionManager* connection_manager = system_state_->connection_manager();
+  ConnectionManagerInterface* connection_manager =
+      system_state_->connection_manager();
   if (!connection_manager->GetConnectionProperties(&dbus_iface,
                                                    &network_connection_type,
                                                    &tethering)) {