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/angle.gyp b/gyp/angle.gyp
index 467c7fb..d555cb9 100644
--- a/gyp/angle.gyp
+++ b/gyp/angle.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.
 # ANGLE is the Windows-specific translator from OGL ES to D3D
 
 {