Fix "unused variable" warnings.

content/browser/loader/mime_type_resource_handler.cc

Index: content/browser/loader/mime_type_resource_handler.cc
diff --git a/content/browser/loader/mime_type_resource_handler.cc b/content/browser/loader/mime_type_resource_handler.cc
index 6cf84d5861205ee1ff0f201ecd904de2f12ae55a..ab4fca3a8dbdc4780fb66e01878e11c1a5aa31eb 100644
--- a/content/browser/loader/mime_type_resource_handler.cc
+++ b/content/browser/loader/mime_type_resource_handler.cc
@@ -73,12 +73,15 @@ MimeTypeResourceHandler::MimeTypeResourceHandler(
     : LayeredResourceHandler(request, std::move(next_handler)),
       state_(STATE_STARTING),
       host_(host),
+#if defined(ENABLE_PLUGINS)
       plugin_service_(plugin_service),
+#endif
       read_buffer_size_(0),
       bytes_read_(0),
       must_download_(false),
       must_download_is_set_(false),
-      weak_ptr_factory_(this) {}
+      weak_ptr_factory_(this) {
+}
 
 MimeTypeResourceHandler::~MimeTypeResourceHandler() {
 }