Add copyright headers to remaining gyp files.

Prevents some PRESUBMIT errors.

TBR=mtklein@google.com

Review URL: https://codereview.chromium.org/1035523003
diff --git a/gyp/flags.gyp b/gyp/flags.gyp
index 50c1a80..6aae30b 100644
--- a/gyp/flags.gyp
+++ b/gyp/flags.gyp
@@ -1,3 +1,7 @@
+# Copyright 2015 Google Inc.
+#
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
 # GYP file to build flag parser
 #
 {