MacViews: Don't exclude app_modal views files on Mac

MacViews browser wants to link with JavaScriptAppModalDialogViews, include
these files on Mac. They are only used when mac_views_browser==1, and will
be pruned out at link time otherwise.

BUG=425229

Review URL: https://codereview.chromium.org/1044253002

Cr-Commit-Position: refs/heads/master@{#323101}
diff --git a/components/app_modal/BUILD.gn b/components/app_modal/BUILD.gn
index 76dad7e..c6b8900a 100644
--- a/components/app_modal/BUILD.gn
+++ b/components/app_modal/BUILD.gn
@@ -30,7 +30,7 @@
     deps += [ "//ui/aura" ]
   }
 
-  if (toolkit_views && !is_mac) {
+  if (toolkit_views) {
     sources += [
       "views/javascript_app_modal_dialog_views.cc",
       "views/javascript_app_modal_dialog_views.h",