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/skia_lib.gyp b/gyp/skia_lib.gyp
index 80d4f8f..8cb5fa1 100644
--- a/gyp/skia_lib.gyp
+++ b/gyp/skia_lib.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.
 # The minimal set of static libraries for basic Skia functionality.
 
 {