Add optional public header checking to GN build

tools/gn/command_check.cc

Index: tools/gn/command_check.cc
diff --git a/tools/gn/command_check.cc b/tools/gn/command_check.cc
new file mode 100644
index 0000000000000000000000000000000000000000..a84bdf3096e2f68ab29030d0b78de088269a6cb4
--- /dev/null
+++ b/tools/gn/command_check.cc
@@ -0,0 +1,40 @@
+// 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 "tools/gn/commands.h"
+#include "tools/gn/setup.h"
+#include "tools/gn/standard_out.h"
+
+namespace commands {
+
+const char kCheck[] = "check";
+const char kCheck_HelpShort[] =
+    "check: Check header dependencies.";
+const char kCheck_Help[] =
+    "gn check: Check header dependencies.\n"
+    "\n"
+    "  \"gn check\" is the same thing as \"gn gen\" with the \"--check\" flag\n"
+    "  except that this command does not write out any build files. It's\n"
+    "  intended to be an easy way to manually trigger include file checking.\n"
+    "\n"
+    "  See \"gn help\" for the common command-line switches.\n";
+
+// Note: partially duplicated in command_gyp.cc.
+int RunCheck(const std::vector<std::string>& args) {
+  // Deliberately leaked to avoid expensive process teardown.
+  Setup* setup = new Setup();
+  // TODO(brettw) bug 343726: Use a temporary directory instead of this
+  // default one to avoid messing up any build that's in there.
+  if (!setup->DoSetup("//out/Default"))
+    return 1;
+  setup->set_check_public_headers(true);
+
+  if (!setup->Run())
+    return 1;
+
+  OutputString("Header dependency check OK\n", DECORATION_GREEN);
+  return 0;
+}
+
+}  // namespace commands