Implement tracking of BUILD.gn files used to define target, toolchain or

tools/gn/string_utils_unittest.cc

Index: tools/gn/string_utils_unittest.cc
diff --git a/tools/gn/string_utils_unittest.cc b/tools/gn/string_utils_unittest.cc
index eb021a8d5c7eb46ac6967766a5da058baa2bd4a5..3b5d047f0e426cd20f22fe9fd68a602eeb55edb6 100644
--- a/tools/gn/string_utils_unittest.cc
+++ b/tools/gn/string_utils_unittest.cc
@@ -17,14 +17,14 @@
 namespace {
 
 bool CheckExpansionCase(const char* input, const char* expected, bool success) {
-  Scope scope(static_cast<const Settings*>(nullptr));
+  Scope scope(static_cast<const Settings*>(nullptr), {});
   int64_t one = 1;
   scope.SetValue("one", Value(nullptr, one), nullptr);
   scope.SetValue("onestring", Value(nullptr, "one"), nullptr);
 
   // Nested scope called "onescope" with a value "one" inside it.
   std::unique_ptr<Scope> onescope(
-      new Scope(static_cast<const Settings*>(nullptr)));
+      new Scope(static_cast<const Settings*>(nullptr), {}));
   onescope->SetValue("one", Value(nullptr, one), nullptr);
   scope.SetValue("onescope", Value(nullptr, std::move(onescope)), nullptr);