Make SK_BUILD_FOR_WIN32 auto-detection work.

gyp/common_conditions.gypi

 # Copyright 2015 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # conditions used in both common.gypi and skia.gyp in chromium
 #
 {
   'defines': [
     'SK_ALLOW_STATIC_GLOBAL_INITIALIZERS=<(skia_static_initializers)',
@@ skipping 47 matching lines @@
     [ 'skia_arch_type == "x86"', {
       'cflags': [
         '-msse2',
         '-mfpmath=sse',
       ],
     }],
 
     [ 'skia_os == "win"',
       {
         'defines': [
-          'SK_BUILD_FOR_WIN32',
           '_CRT_SECURE_NO_WARNINGS',
           'GR_GL_FUNCTION_TYPE=__stdcall',
           '_HAS_EXCEPTIONS=0',
           'WIN32_LEAN_AND_MEAN',
           'NOMINMAX',
         ],
         'msvs_disabled_warnings': [
             4275,  # An exported class was derived from a class that was not exported
             4345,  # This is an FYI about a behavior change from long ago. Chrome stifles it too.
             4355,  # 'this' used in base member initializer list. Off by default in newer compilers.
@@ skipping 625 matching lines @@
           'LD_RUNPATH_SEARCH_PATHS': ['@executable_path/.'],
       },
     }],
 
   ], # end 'conditions'
   # The Xcode SYMROOT must be at the root. See build/common.gypi in chromium for more details
   'xcode_settings': {
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }