Fix build break on ChromeOS

Test protobufs need to be generated in "brillo" directory now, not
in "chromeos" to match the include paths.

BUG: 24872993
Change-Id: Ib04473b1395f67fead866e2d0e478835b904fb75
diff --git a/libchromeos.gypi b/libchromeos.gypi
index 7e58063..8226828 100644
--- a/libchromeos.gypi
+++ b/libchromeos.gypi
@@ -281,7 +281,7 @@
             'deps': [
               'libchrome-test-<(libbase_ver)',
             ],
-            'proto_in_dir': 'chromeos/dbus',
+            'proto_in_dir': 'brillo/dbus',
             'proto_out_dir': 'include/unittests',
           },
           'includes': [