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.

Change-Id: I93214f6ffb8662c238b3351e52bf2bdf23e46a9c
diff --git a/binder_service_brillo.h b/binder_service_brillo.h
index b3bb81f..fad0f8c 100644
--- a/binder_service_brillo.h
+++ b/binder_service_brillo.h
@@ -19,6 +19,7 @@
 
 #include <utils/Errors.h>
 
+#include <memory>
 #include <string>
 #include <vector>
 
@@ -68,6 +69,10 @@
                                      bool powerwash) override;
   android::binder::Status GetChannel(bool get_current_channel,
                                      android::String16* out_channel) override;
+  android::binder::Status SetCohortHint(
+      const android::String16& cohort_hint) override;
+  android::binder::Status GetCohortHint(
+      android::String16* out_cohort_hint) override;
   android::binder::Status SetP2PUpdatePermission(bool enabled) override;
   android::binder::Status GetP2PUpdatePermission(
       bool* out_p2p_permission) override;