Add copyright headers to remaining gyp files.

gyp/etc1.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.
 {
   'variables': {
     'skia_warnings_as_errors': 0,
   },
   'targets': [
   {
     'target_name': 'libetc1',
     'type': 'static_library',
     'include_dirs' : [
       '../third_party/etc1'
     ],
     'sources': [
       '../third_party/etc1/etc1.cpp',
     ],
     'direct_dependent_settings': {
       'include_dirs': [
         '../third_party/etc1',
       ],
     },
   }],
 }