Make the Windows multi_dll build work in GN

chrome/common/extensions/api/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/json_schema_api.gni")
 import("schemas.gni")
 
 assert(enable_extensions)
 
 # GYP version: chrome/common/extensions/api/api.gyp:chrome_api
@@ skipping 21 matching lines @@
     "//components/copresence/proto",
     "//components/metrics/proto",
     "//skia",
     "//sync",
     "//ui/accessibility:ax_gen",
   ]
   if (is_chromeos) {
     # deps += [ "<(DEPTH)/chrome/chrome.gyp:drive_proto" ]  TODO(GYP)
   }
   deps += schema_dependencies
+
+  # This must be a static library because the generated schemas have
+  # dependencies into both the browser and child processes, and this won't link
+  # in the multi DLL build. In the child DLL, only some files are needed, and
+  # these have no dependencies into the browser, so a static library solves the
+  # problem.
+  generate_static_library = true
 }