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

tools/gn/substitution_writer_unittest.cc

Index: tools/gn/substitution_writer_unittest.cc
diff --git a/tools/gn/substitution_writer_unittest.cc b/tools/gn/substitution_writer_unittest.cc
index d98d4cee5f5ef18060d2c28e437f081c72e042e9..0bf27e86b7771f5b019c1207550b8636abea1f21 100644
--- a/tools/gn/substitution_writer_unittest.cc
+++ b/tools/gn/substitution_writer_unittest.cc
@@ -106,7 +106,7 @@ TEST(SubstitutionWriter, SourceSubstitutions) {
   TestWithScope setup;
   Err err;
 
-  Target target(setup.settings(), Label(SourceDir("//foo/bar/"), "baz"));
+  Target target(setup.settings(), Label(SourceDir("//foo/bar/"), "baz"), {});
   target.set_output_type(Target::STATIC_LIBRARY);
   target.SetToolchain(setup.toolchain());
   ASSERT_TRUE(target.OnResolved(&err));
@@ -197,7 +197,7 @@ TEST(SubstitutionWriter, TargetSubstitutions) {
   TestWithScope setup;
   Err err;
 
-  Target target(setup.settings(), Label(SourceDir("//foo/bar/"), "baz"));
+  Target target(setup.settings(), Label(SourceDir("//foo/bar/"), "baz"), {});
   target.set_output_type(Target::STATIC_LIBRARY);
   target.SetToolchain(setup.toolchain());
   ASSERT_TRUE(target.OnResolved(&err));
@@ -236,7 +236,7 @@ TEST(SubstitutionWriter, CompilerSubstitutions) {
   TestWithScope setup;
   Err err;
 
-  Target target(setup.settings(), Label(SourceDir("//foo/bar/"), "baz"));
+  Target target(setup.settings(), Label(SourceDir("//foo/bar/"), "baz"), {});
   target.set_output_type(Target::STATIC_LIBRARY);
   target.SetToolchain(setup.toolchain());
   ASSERT_TRUE(target.OnResolved(&err));
@@ -257,7 +257,7 @@ TEST(SubstitutionWriter, LinkerSubstitutions) {
   TestWithScope setup;
   Err err;
 
-  Target target(setup.settings(), Label(SourceDir("//foo/bar/"), "baz"));
+  Target target(setup.settings(), Label(SourceDir("//foo/bar/"), "baz"), {});
   target.set_output_type(Target::SHARED_LIBRARY);
   target.SetToolchain(setup.toolchain());
   ASSERT_TRUE(target.OnResolved(&err));
@@ -310,7 +310,7 @@ TEST(SubstitutionWriter, OutputDir) {
   tool.SetComplete();
 
   // Default target with no output dir overrides.
-  Target target(setup.settings(), Label(SourceDir("//foo/"), "baz"));
+  Target target(setup.settings(), Label(SourceDir("//foo/"), "baz"), {});
   target.set_output_type(Target::EXECUTABLE);
   target.SetToolchain(setup.toolchain());
   ASSERT_TRUE(target.OnResolved(&err));