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

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")
 
 declare_args() {
   # When set, turns off the (normally-on) iterator debugging and related stuff
   # that is normally turned on for Debug builds. These are generally useful for
   # catching bugs but in some cases may cause conflicts or excessive slowness.
   disable_iterator_debugging = false
@@ skipping 322 matching lines @@
       "CoreFoundation.framework",
       "CoreGraphics.framework",
       "CoreText.framework",
       "Foundation.framework",
       "UIKit.framework",
     ]
   } else if (is_linux) {
     libs = [ "dl" ]
   }
 }