Fix windows pdfium_use_skia build.

skia/skia_common.gypi

 # Copyright 2013 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.
 
 # This gypi file handles the removal of platform-specific files from the
 # Skia build.
 {
   'include_dirs': [
     '..',
     'config',
   ],
 
   'conditions': [
     [ 'OS != "android"', {
       'sources/': [
          ['exclude', '_android\\.(cc|cpp)$'],
       ],
     }],
     [ 'OS != "ios"', {
       'sources/': [
          ['exclude', '_ios\\.(cc|cpp|mm?)$'],
       ],
     }],
     [ 'OS == "ios"', {
       'defines': [
         'SK_BUILD_FOR_IOS',
       ],
     }],
+    [ 'OS == "win"', {
+      'defines': [
+        'SK_BUILD_FOR_WIN32',
+      ],
+    }],
     [ 'OS != "mac"', {
       'sources/': [
         ['exclude', '_mac\\.(cc|cpp|mm?)$'],
       ],
     }],
     [ 'OS == "mac"', {
       'defines': [
         'SK_BUILD_FOR_MAC',
       ],
     }],
@@ skipping 109 matching lines @@
   # re-export if they include Skia headers in their public headers.
   'all_dependent_settings': {
     'include_dirs': [
       '..',
       'config',
     ],
   },
 
   'msvs_disabled_warnings': [4244, 4267, 4341, 4345, 4390, 4554, 4748, 4800],
 }