Add a GN flag for the Windows multi-dll build.

third_party/harfbuzz-ng/BUILD.gn

 # Copyright 2014 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/chrome_build.gni")
 import("//build/config/linux/pkg_config.gni")
 
 # The GYP build supports system harfbuzz for non-official builds when using
 # pangoft2 1.31.0 or greater (which pulls it in).
 # TODO(brettw) we can consider doing this as well, although the benefit is
 # unclear and requires shelling out to a script to check the version.
 #
 # ChromeOS uses an up-to-date system one that we have control over, so we
 # don't want to bloat the binary more by including another copy.
 
@@ skipping 143 matching lines @@
     }
     if (is_mac) {
       sources += [
         "src/hb-coretext.cc",
         "src/hb-coretext.h",
       ]
       defines += [ "HAVE_CORETEXT" ]
     }
   }
 }