Pepper: Change '*_sources' variables in ppapi_sources.gypi to '*_source_files'.

ppapi/ppapi_cpp.gypi

 # Copyright (c) 2011 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Shared source lists between trusted and untrusted targets are stored in 
 # ppapi_sources.gypi.
 
 {
   'includes': [
     'ppapi_sources.gypi',
   ],
   'targets': [
     {
       'target_name': 'ppapi_c',
       'type': 'none',
       'all_dependent_settings': {
         'include_dirs+': [
           '..',
         ],
       },
       'sources': [
-        '<@(c_sources)',
+        '<@(c_source_files)',
       ],
     },
     {
       'target_name': 'ppapi_cpp_objects',
       'type': 'static_library',
       'dependencies': [
         'ppapi_c'
       ],
       'include_dirs+': [
         '..',
       ],
       'sources': [
-        '<@(cpp_sources)',
+        '<@(cpp_source_files)',
       ],
       'conditions': [
         ['OS=="win"', {
           'msvs_settings': {
             'VCCLCompilerTool': {
               'AdditionalOptions': ['/we4244'],  # implicit conversion, possible loss of data
             },
           },
         }],
         ['OS=="linux"', {
@@ skipping 26 matching lines @@
         }],
         ['OS=="mac"', {
           'xcode_settings': {
             'WARNING_CFLAGS': ['-Wextra', '-pedantic'],
            },
         }]
       ],
     },
   ],
 }