Make `display_list/...` compatible with `.clang_tidy`. (#47993)

Work towards https://github.com/flutter/flutter/issues/134969.

All changes were made automatically (i.e. with `--fix`).
diff --git a/display_list/effects/dl_color_source.h b/display_list/effects/dl_color_source.h
index 094006e..39359d7 100644
--- a/display_list/effects/dl_color_source.h
+++ b/display_list/effects/dl_color_source.h
@@ -644,7 +644,7 @@
         uniform_data_(std::move(uniform_data)) {}
 
   bool isUIThreadSafe() const override {
-    for (auto sampler : samplers_) {
+    for (const auto& sampler : samplers_) {
       if (!sampler->isUIThreadSafe()) {
         return false;
       }