diff --git a/base/strings/gn_deps_debugging_eval.cc b/base/strings/gn_deps_debugging_eval.cc
new file mode 100644
index 0000000000000..801d9a7fabcde
--- /dev/null
+++ b/base/strings/gn_deps_debugging_eval.cc
@@ -0,0 +1,17 @@
+// Copyright 2026 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/strings/gn_deps_debugging_eval.h"
+
+namespace base::gn_deps_debugging_eval {
+
+FooController::FooController(PrefService* prefs) : prefs_(prefs) {}
+
+FooController::~FooController() = default;
+
+bool FooController::HasPrefsForTesting() const {
+  return prefs_ != nullptr;
+}
+
+}  // namespace base::gn_deps_debugging_eval
diff --git a/base/strings/gn_deps_debugging_eval.h b/base/strings/gn_deps_debugging_eval.h
new file mode 100644
index 0000000000000..d5f7b706abcde
--- /dev/null
+++ b/base/strings/gn_deps_debugging_eval.h
@@ -0,0 +1,28 @@
+// Copyright 2026 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_STRINGS_GN_DEPS_DEBUGGING_EVAL_H_
+#define BASE_STRINGS_GN_DEPS_DEBUGGING_EVAL_H_
+
+#include "components/prefs/pref_service.h"
+
+namespace base::gn_deps_debugging_eval {
+
+// This fake class is used by //agents prompt evals. The include above creates
+// a GN include-visibility problem because this public header only needs a
+// pointer declaration.
+class FooController {
+ public:
+  explicit FooController(PrefService* prefs);
+  ~FooController();
+
+  bool HasPrefsForTesting() const;
+
+ private:
+  PrefService* prefs_;
+};
+
+}  // namespace base::gn_deps_debugging_eval
+
+#endif  // BASE_STRINGS_GN_DEPS_DEBUGGING_EVAL_H_