update_engine: Use org.chromium.KioskAppService service.

Make update_engine use the org.chromium.KioskAppService
D-Bus service exported by Chrome rather than the old methods
under org.chromium.LibCrosService.

BUG=chromium:703229
TEST=unit tests pass; also hacked up RealSystemProvider to
     call its GetKioskAppRequiredPlatformVersion and
     manually verified that the D-Bus call succeeds

Change-Id: I02d503da1e1aec2319c75e2237c87bfcdcd1f7e5
Reviewed-on: https://chromium-review.googlesource.com/987325
Commit-Ready: Dan Erat <derat@chromium.org>
Tested-by: Dan Erat <derat@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
diff --git a/dbus_bindings/org.chromium.KioskAppService.dbus-xml b/dbus_bindings/org.chromium.KioskAppService.dbus-xml
new file mode 100644
index 0000000..11b888b
--- /dev/null
+++ b/dbus_bindings/org.chromium.KioskAppService.dbus-xml
@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+
+<node name="/org/chromium/KioskAppService"
+      xmlns:tp="http://telepathy.freedesktop.org/wiki/DbusSpec#extensions-v0">
+  <interface name="org.chromium.KioskAppServiceInterface">
+    <method name="GetRequiredPlatformVersion">
+      <arg name="required_platform_version" type="s" direction="out" />
+    </method>
+  </interface>
+</node>
diff --git a/dbus_bindings/org.chromium.LibCrosService.dbus-xml b/dbus_bindings/org.chromium.LibCrosService.dbus-xml
deleted file mode 100644
index 3111c63..0000000
--- a/dbus_bindings/org.chromium.LibCrosService.dbus-xml
+++ /dev/null
@@ -1,10 +0,0 @@
-<?xml version="1.0" encoding="UTF-8" ?>
-
-<node name="/org/chromium/LibCrosService"
-      xmlns:tp="http://telepathy.freedesktop.org/wiki/DbusSpec#extensions-v0">
-  <interface name="org.chromium.LibCrosServiceInterface">
-    <method name="GetKioskAppRequiredPlatformVersion">
-      <arg name="required_platform_version" type="s" direction="out" />
-    </method>
-  </interface>
-</node>