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

content/app/BUILD.gn

Index: content/app/BUILD.gn
diff --git a/content/app/BUILD.gn b/content/app/BUILD.gn
index f6c72b9f86427fa64c53669074d43f026b48682b..8da75d4ff61ccc29a02cf9cf3952634b111c62a9 100644
--- a/content/app/BUILD.gn
+++ b/content/app/BUILD.gn
@@ -2,8 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-# TODO(GYP) enable chrome_multiple_dll support
-is_chrome_multiple_dll = false
+import("//build/config/chrome_build.gni")
 
 content_app_sources = [
   "android/app_jni_registrar.cc",
@@ -71,7 +70,7 @@ content_app_extra_configs = [
   "//content:content_implementation",
 ]
 
-if (!is_chrome_multiple_dll) {
+if (!is_multi_dll_chrome) {
   content_app_deps += [ "//content/gpu:gpu_sources" ]
 }
 
@@ -86,7 +85,7 @@ source_set("both") {
   deps = content_app_deps
 }
 
-if (is_chrome_multiple_dll) {
+if (is_multi_dll_chrome) {
   # It doesn't make sense to do the browser/child dll split in component mode.
   assert(!is_component_build)
 
@@ -97,7 +96,7 @@ if (is_chrome_multiple_dll) {
     configs += content_app_extra_configs
     deps = content_app_deps
 
-    defines += [ "CHROME_MULTIPLE_DLL_BROWSER" ]
+    defines = [ "CHROME_MULTIPLE_DLL_BROWSER" ]
   }
 
   source_set("child") {
@@ -107,6 +106,6 @@ if (is_chrome_multiple_dll) {
     configs += content_app_extra_configs
     deps = content_app_deps
 
-    defines += [ "CHROME_MULTIPLE_DLL_CHILD" ]
+    defines = [ "CHROME_MULTIPLE_DLL_CHILD" ]
   }
 }