update_engine: Change parameters of AttemptInstall() DBus

Currently, the update_engine is using the dlcservice's protobuf as
its own input. This is bad API because now anyone dependent on the
update_engine's DBus, needs to be dependent on the dlcservice too. This
CL changes that so we only pass the arguments we want (DLC DIs and the
omaha url).

BUG=chromium:1071654
TEST=cros_workon_make --board reef --test update_engine

Cq-Depend: chromium:2157670
Change-Id: Id7f7a86d8b3e3194d4d7697a8ad26ed4bcc4ba2c
Reviewed-on: https://chromium-review.googlesource.com/c/aosp/platform/system/update_engine/+/2163442
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Andrew Lassalle <andrewlassalle@chromium.org>
Reviewed-by: Jae Hoon Kim <kimjae@chromium.org>
Commit-Queue: Amin Hassani <ahassani@chromium.org>
diff --git a/dbus_bindings/org.chromium.UpdateEngineInterface.dbus-xml b/dbus_bindings/org.chromium.UpdateEngineInterface.dbus-xml
index 51457e5..ac2f021 100644
--- a/dbus_bindings/org.chromium.UpdateEngineInterface.dbus-xml
+++ b/dbus_bindings/org.chromium.UpdateEngineInterface.dbus-xml
@@ -35,12 +35,11 @@
       <arg type="i" name="flags" direction="in" />
     </method>
     <method name="AttemptInstall">
-      <arg type="ay" name="request" direction="in">
+      <arg type="s" name="omaha_url" direction="in" />
+      <arg type="as" name="dlc_ids" direction="in">
         <tp:docstring>
-          The information about DLC modules that needs to be installed.
+          The list of DLC IDs that needs to be installed.
         </tp:docstring>
-        <annotation name="org.chromium.DBus.Argument.ProtobufClass"
-                    value="dlcservice::DlcModuleList"/>
       </arg>
     </method>
     <method name="AttemptRollback">