Add missing .h files to .gn files that have a .cc file next to it in the gn file already.

components/constrained_window/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/ui.gni")
 import("//ui/base/ui_features.gni")
 
 static_library("constrained_window") {
   sources = [
     "constrained_window_views.cc",
     "constrained_window_views.h",
     "constrained_window_views_client.h",
     "native_web_contents_modal_dialog_manager_views.cc",
     "native_web_contents_modal_dialog_manager_views.h",
+    "native_web_contents_modal_dialog_manager_views_mac.h",
     "native_web_contents_modal_dialog_manager_views_mac.mm",
   ]
 
   if (is_mac && !mac_views_browser) {
     sources += [ "show_modal_dialog_cocoa.cc" ]
   } else {
     sources += [ "show_modal_dialog_views.cc" ]
   }
 
   deps = [
@@ skipping 25 matching lines @@
   if (is_mac && !mac_views_browser) {
     sources += [ "test_create_native_web_modal_manager_cocoa.cc" ]
   }
 
   deps = [
     ":constrained_window",
     "//components/web_modal:test_support",
     "//ui/views:test_support",
   ]
 }