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/update_attempter.h b/update_attempter.h
index 193e172..082ebfe 100644
--- a/update_attempter.h
+++ b/update_attempter.h
@@ -29,9 +29,9 @@
 #include <base/time/time.h>
 #include <gtest/gtest_prod.h>  // for FRIEND_TEST
 
-#if USE_LIBCROS
+#if USE_CHROME_NETWORK_PROXY
 #include "update_engine/chrome_browser_proxy_resolver.h"
-#endif  // USE_LIBCROS
+#endif  // USE_CHROME_NETWORK_PROXY
 #include "update_engine/certificate_checker.h"
 #include "update_engine/client_library/include/update_engine/update_status.h"
 #include "update_engine/common/action_processor.h"
@@ -307,13 +307,13 @@
   void MarkDeltaUpdateFailure();
 
   ProxyResolver* GetProxyResolver() {
-#if USE_LIBCROS
+#if USE_CHROME_NETWORK_PROXY
     return obeying_proxies_ ?
         reinterpret_cast<ProxyResolver*>(&chrome_proxy_resolver_) :
         reinterpret_cast<ProxyResolver*>(&direct_proxy_resolver_);
 #else
     return &direct_proxy_resolver_;
-#endif  // USE_LIBCROS
+#endif  // USE_CHROME_NETWORK_PROXY
   }
 
   // Sends a ping to Omaha.
@@ -455,9 +455,9 @@
 
   // Our two proxy resolvers
   DirectProxyResolver direct_proxy_resolver_;
-#if USE_LIBCROS
+#if USE_CHROME_NETWORK_PROXY
   ChromeBrowserProxyResolver chrome_proxy_resolver_;
-#endif  // USE_LIBCROS
+#endif  // USE_CHROME_NETWORK_PROXY
 
   // Originally, both of these flags are false. Once UpdateBootFlags is called,
   // |update_boot_flags_running_| is set to true. As soon as UpdateBootFlags