Guard dbus component and config with assert(use_dbus)

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 308243a275da875ffe16145e2c8d80abc7d0b7fc..1bd956e34d64076953576894f487ede9a98a85d5 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -401,8 +401,6 @@ group("both_gn_and_gyp") {
     deps += [
       "//chrome:manpage",
       "//chrome:xdg_mime",
-      "//dbus:dbus_test_server",
-      "//dbus:dbus_unittests",
       "//net:disk_cache_memory_test",
       "//net:flip_in_mem_edsm_server",
       "//net:flip_in_mem_edsm_server_unittests",
@@ -412,6 +410,13 @@ group("both_gn_and_gyp") {
       "//sandbox/linux:sandbox_linux_unittests",
     ]
 
+    if (use_dbus) {
+      deps += [
+        "//dbus:dbus_test_server",
+        "//dbus:dbus_unittests",
+      ]
+    }
+
     if (is_chromeos || use_ash) {
       deps += [ "//components/session_manager/core" ]
     }