Add copyright headers to remaining gyp files.

gyp/pdf.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.
 # This file builds the PDF backend.
 {
   'targets': [
     {
       'target_name': 'pdf',
       'product_name': 'skia_pdf',
       'type': 'static_library',
       'standalone_static_library': 1,
       'dependencies': [
         'skia_lib.gyp:skia_lib',
@@ skipping 30 matching lines @@
         'defines': [
           'SK_SUPPORT_PDF',
         ],
         'include_dirs': [
           '../include/core',  # SkDocument.h
         ],
       },
     },
   ],
 }