update_engine: Breaks the use of libcros into two dbus proxies.

This CL breaks USE_LIBCROS into two defines:
	USE_CHROME_NETWORK_PROXY
	USE_CHROME_KIOSK_APP
and changes all related build artifacts for both chrome and android.

Breaks USE_libcros into USE_chrome_network_proxy and USE_chrome_kiosk_app.
Removes BRILL_USE_LIBCROS.
Replaces __BRILLO__ with USE_OMAHA.

BUG=chromium:717306
TEST=Ran test 'cros_workon_make --board=amd64-generic --test update_engine'
	for all four conditions of the newly introduced two flags.

Change-Id: I9ca5b35c22a17c45a861db6a434239096a896127
Reviewed-on: https://chromium-review.googlesource.com/596802
Commit-Ready: Amin Hassani <ahassani@chromium.org>
Tested-by: Amin Hassani <ahassani@chromium.org>
Tested-by: Sen Jiang <senj@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Sen Jiang <senj@chromium.org>
diff --git a/real_system_state.h b/real_system_state.h
index 64964cd..6aee0af 100644
--- a/real_system_state.h
+++ b/real_system_state.h
@@ -25,10 +25,12 @@
 #include <metrics/metrics_library.h>
 #include <policy/device_policy.h>
 
-#if USE_LIBCROS
+#if USE_CHROME_KIOSK_APP
 #include <libcros/dbus-proxies.h>
+#endif  // USE_CHROME_KIOSK_APP
+#if USE_CHROME_NETWORK_PROXY
 #include <network_proxy/dbus-proxies.h>
-#endif  // USE_LIBCROS
+#endif  // USE_CHROME_NETWORK_PROXY
 
 #include "update_engine/certificate_checker.h"
 #include "update_engine/common/boot_control_interface.h"
@@ -127,12 +129,14 @@
   inline bool system_rebooted() override { return system_rebooted_; }
 
  private:
-#if USE_LIBCROS
   // Real DBus proxies using the DBus connection.
+#if USE_CHROME_KIOSK_APP
   std::unique_ptr<org::chromium::LibCrosServiceInterfaceProxy> libcros_proxy_;
+#endif  // USE_CHROME_KIOSK_APP
+#if USE_CHROME_NETWORK_PROXY
   std::unique_ptr<org::chromium::NetworkProxyServiceInterfaceProxy>
       network_proxy_service_proxy_;
-#endif  // USE_LIBCROS
+#endif  // USE_CHROME_NETWORK_PROXY
 
   // Interface for the power manager.
   std::unique_ptr<PowerManagerInterface> power_manager_;