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

content/test/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/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//build/module_args/v8.gni")
 import("//testing/test.gni")
 import("//third_party/mojo/src/mojo/public/tools/bindings/mojom.gni")
 
 content_tests_gypi_values =
     exec_script("//build/gypi_to_gn.py",
                 [
@@ skipping 695 matching lines @@
       "//gpu/blink",
       "//testing/gtest",
       "//third_party/WebKit/public:blink",
       "//ui/base",
       "//ui/gfx",
       "//ui/gfx/geometry",
       "//ui/gl",
     ]
   }
 }