buffet: Add ObjectManager interface to /org/chromium/Buffet

BUG=chromium:359190
TEST=`buffet_client GetManagedObjects` returns
message_type: MESSAGE_METHOD_RETURN
destination: :1.35
sender: :1.31
signature: a{oa{sa{sv}}}
serial: 10
reply_serial: 3

array [
  dict entry {
    object_path "/org/chromium/Buffet/Manager"
    array [
      dict entry {
        string "org.chromium.Buffet.Manager"
        array [
          dict entry {
            string "State"
            variant               string "{}"
          }
        ]
      }
    ]
  }
]

Done.

Change-Id: I2bbcc9a3f71c7ec6ab76cb4600dad7efe1a8bb0a
Reviewed-on: https://chromium-review.googlesource.com/198963
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: Christopher Wiley <wiley@chromium.org>
Tested-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: Ilja Friedel <ihf@chromium.org>
diff --git a/buffet/exported_object_manager.cc b/buffet/exported_object_manager.cc
index 6458128..c1403ad 100644
--- a/buffet/exported_object_manager.cc
+++ b/buffet/exported_object_manager.cc
@@ -12,10 +12,9 @@
 
 namespace dbus_utils {
 
-ExportedObjectManager::ExportedObjectManager(dbus::Bus* bus,
+ExportedObjectManager::ExportedObjectManager(scoped_refptr<dbus::Bus> bus,
                                              const dbus::ObjectPath& path)
-    : bus_(bus), exported_object_(bus->GetExportedObject(path)),
-      weak_ptr_factory_(this) {}
+    : bus_(bus), exported_object_(bus->GetExportedObject(path)) {}
 
 void ExportedObjectManager::Init(const OnInitFinish& cb) {
   bus_->AssertOnOriginThread();
@@ -25,12 +24,13 @@
       dbus::kObjectManagerInterface,
       dbus::kObjectManagerGetManagedObjects,
       base::Bind(&ExportedObjectManager::HandleGetManagedObjects,
-                 weak_ptr_factory_.GetWeakPtr()),
+                 AsWeakPtr()),
       sequencer->GetExportHandler(
           dbus::kObjectManagerInterface,
           dbus::kObjectManagerGetManagedObjects,
           "Failed exporting GetManagedObjects method of ObjectManager",
           false));
+  sequencer->OnAllTasksCompletedCall({cb});
 }
 
 void ExportedObjectManager::ClaimInterface(