Patch 2: Added a preprocessor flag for platform spellcheck.

build/config/BUILD.gn

 # Copyright (c) 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.
 
 import("//build/config/allocator.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//build/module_args/v8.gni")
@@ skipping 62 matching lines @@
     }
     if (enable_print_preview) {
       # Enable printing with print preview.
       # Can be defined without ENABLE_BASIC_PRINTING.
       defines += [ "ENABLE_PRINT_PREVIEW=1" ]
     }
   }
   if (enable_spellcheck) {
     defines += [ "ENABLE_SPELLCHECK=1" ]
   }
+  if (use_platform_spellchecker) {
+    defines += [ "USE_PLATFORM_SPELLCHECKER=1" ]
+  }
   if (dont_embed_build_metadata) {
     defines += [ "DONT_EMBED_BUILD_METADATA" ]
   }
   if (dcheck_always_on) {
     defines += [ "DCHECK_ALWAYS_ON=1" ]
   }
   if (use_udev) {
     # TODO(brettw) should probably be "=1".
     defines += [ "USE_UDEV" ]
   }
@@ skipping 324 matching lines @@
 
     # This is a file that GN will compile with the above header. It will be
     # implicitly added to the sources (potentially multiple times, with one
     # variant for each language used in the target).
     precompiled_source = "//build/precompile.cc"
 
     # Force include the header.
     cflags = [ "/FI$precompiled_header" ]
   }
 }