Move web modal dialog manager files into the constrained_window component.

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")
+
 source_set("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",
   ]
 
+  if (is_mac && !mac_views_browser) {
+    sources += [ "show_modal_dialog_cocoa.cc" ]
+  } else {
+    sources += [ "show_modal_dialog_views.cc" ]
+  }
+
   deps = [
     "//components/guest_view/browser",
     "//components/web_modal",
-    "//skia",
+    "//content/public/browser",
     "//ui/views",
   ]
+  public_deps = [
+    # Skia headers are exposed in the public API.
+    "//skia",
+  ]
+
+  if (use_aura) {
+    deps += [
+      "//ui/aura",
+      "//ui/wm",
+    ]
+  }
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "constrained_window_views_unittest.cc",
   ]
 
+  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",
   ]
 }