Support notifications with custom content

ui/message_center/BUILD.gn

Index: ui/message_center/BUILD.gn
diff --git a/ui/message_center/BUILD.gn b/ui/message_center/BUILD.gn
index 11dae432ddd26a6efdb06e65ebbf7ec76c41bad8..c878f4f7b08c1011c0d189ba55c5104ad43417e4 100644
--- a/ui/message_center/BUILD.gn
+++ b/ui/message_center/BUILD.gn
@@ -94,9 +94,12 @@ component("message_center") {
     # with message_center_unittests below.
     if (toolkit_views && !is_mac) {
       sources += [
+        "notification_delegate_views.cc",
         "views/bounded_label.cc",
         "views/bounded_label.h",
         "views/constants.h",
+        "views/custom_notification_view.cc",
+        "views/custom_notification_view.h",
         "views/desktop_popup_alignment_delegate.cc",
         "views/desktop_popup_alignment_delegate.h",
         "views/message_bubble_base.cc",
@@ -116,6 +119,8 @@ component("message_center") {
         "views/message_view.h",
         "views/message_view_context_menu_controller.cc",
         "views/message_view_context_menu_controller.h",
+        "views/message_view_factory.cc",
+        "views/message_view_factory.h",
         "views/notification_button.cc",
         "views/notification_button.h",
         "views/notification_progress_bar.cc",
@@ -232,6 +237,7 @@ test("message_center_unittests") {
     if (toolkit_views && !is_mac) {
       sources += [
         "views/bounded_label_unittest.cc",
+        "views/custom_notification_view_unittest.cc",
         "views/message_center_view_unittest.cc",
         "views/message_popup_collection_unittest.cc",
         "views/notification_view_unittest.cc",