Add copyright headers to remaining gyp files.

gyp/nacl.gyp

+# Copyright 2015 Google Inc.
+#
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
 # Common entry point for all Skia executables running in NaCl
 {
   'targets': [
     {
       'target_name': 'nacl_interface',
       'type': 'static_library',
       'dependencies': [
         'skia_lib.gyp:skia_lib',
       ],
       'include_dirs': [
         # For SkThreadUtils.h
         '../src/utils',
       ],
       'sources': [
         '../platform_tools/nacl/src/nacl_interface.cpp',
       ],
     },
   ],
 }