Add initial prototype for the GN meta-buildsystem.

tools/gn/target_generator_unittest.cc

Index: tools/gn/target_generator_unittest.cc
diff --git a/ui/base/models/dialog_model.cc b/tools/gn/target_generator_unittest.cc
similarity index 57%
copy from ui/base/models/dialog_model.cc
copy to tools/gn/target_generator_unittest.cc
index 310bff04c5027dee495cf98b5f4512dda1a3fc46..feef6a96912e4ee6bfba691afbf5fa5a0bbffe77 100644
--- a/ui/base/models/dialog_model.cc
+++ b/tools/gn/target_generator_unittest.cc
@@ -2,11 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "ui/base/models/dialog_model.h"
+#include "testing/gtest/include/gtest/gtest.h"
+#include "tools/gn/filesystem_utils.h"
+#include "tools/gn/target_generator.h"
 
-namespace ui {
-
-DialogModel::~DialogModel() {
-}
-
-}  // namespace ui