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

tools/gn/ninja_group_target_writer_unittest.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "testing/gtest/include/gtest/gtest.h"
 #include "tools/gn/ninja_group_target_writer.h"
 #include "tools/gn/target.h"
 #include "tools/gn/test_with_scope.h"
 
 TEST(NinjaGroupTargetWriter, Run) {
   Err err;
   TestWithScope setup;
 
-  Target target(setup.settings(), Label(SourceDir("//foo/"), "bar"));
+  Target target(setup.settings(), Label(SourceDir("//foo/"), "bar"), {});
   target.set_output_type(Target::GROUP);
   target.visibility().SetPublic();
 
-  Target dep(setup.settings(), Label(SourceDir("//foo/"), "dep"));
+  Target dep(setup.settings(), Label(SourceDir("//foo/"), "dep"), {});
   dep.set_output_type(Target::ACTION);
   dep.visibility().SetPublic();
   dep.SetToolchain(setup.toolchain());
   ASSERT_TRUE(dep.OnResolved(&err));
 
-  Target dep2(setup.settings(), Label(SourceDir("//foo/"), "dep2"));
+  Target dep2(setup.settings(), Label(SourceDir("//foo/"), "dep2"), {});
   dep2.set_output_type(Target::ACTION);
   dep2.visibility().SetPublic();
   dep2.SetToolchain(setup.toolchain());
   ASSERT_TRUE(dep2.OnResolved(&err));
 
-  Target datadep(setup.settings(), Label(SourceDir("//foo/"), "datadep"));
+  Target datadep(setup.settings(), Label(SourceDir("//foo/"), "datadep"), {});
   datadep.set_output_type(Target::ACTION);
   datadep.visibility().SetPublic();
   datadep.SetToolchain(setup.toolchain());
   ASSERT_TRUE(datadep.OnResolved(&err));
 
   target.public_deps().push_back(LabelTargetPair(&dep));
   target.public_deps().push_back(LabelTargetPair(&dep2));
   target.data_deps().push_back(LabelTargetPair(&datadep));
 
   target.SetToolchain(setup.toolchain());
   ASSERT_TRUE(target.OnResolved(&err));
 
   std::ostringstream out;
   NinjaGroupTargetWriter writer(&target, out);
   writer.Run();
 
   const char expected[] =
       "build obj/foo/bar.stamp: stamp obj/foo/dep.stamp obj/foo/dep2.stamp || obj/foo/datadep.stamp\n";
   EXPECT_EQ(expected, out.str());
 }