Add {Get,Set}CohortHint interface.

Export the "cohort hint" getter and setter in the client interfaces
(D-Bus and Binder). The cohort hint is sent to Omaha on every update
check request but can be ignored and/or reset by Omaha on every
response.

Other minor linter fixes to the affected files.

Bug: 31740109
Test: Build with D-Bus and with Binder.

(cherry picked from commit 5b5fa8b412312a41cfd4d7ab475b54d4f730ed2a)

Change-Id: Ieb40c2d4bbe2ce926d54b6348b22f2840d8327db
Reviewed-on: https://chromium-review.googlesource.com/395206
Commit-Ready: Alex Deymo <deymo@chromium.org>
Tested-by: Alex Deymo <deymo@chromium.org>
Reviewed-by: Christopher Book <cbook@chromium.org>
diff --git a/dbus_bindings/org.chromium.UpdateEngineInterface.dbus-xml b/dbus_bindings/org.chromium.UpdateEngineInterface.dbus-xml
index aa99508..848f775 100644
--- a/dbus_bindings/org.chromium.UpdateEngineInterface.dbus-xml
+++ b/dbus_bindings/org.chromium.UpdateEngineInterface.dbus-xml
@@ -44,6 +44,12 @@
       <arg type="b" name="get_current_channel" direction="in" />
       <arg type="s" name="channel" direction="out" />
     </method>
+    <method name="SetCohortHint">
+      <arg type="s" name="cohort_hint" direction="in" />
+    </method>
+    <method name="GetCohortHint">
+      <arg type="s" name="cohort_hint" direction="out" />
+    </method>
     <method name="SetP2PUpdatePermission">
       <annotation name="org.freedesktop.DBus.GLib.CSymbol"
         value="update_engine_service_set_p2p_update_permission" />