UserAgent: Mozilla/5.0 (X11; Linux x86_64; rv:47.0) Gecko/20100101 Firefox/47.0

Steps to reproduce the problem:
1. Use GTK+ 3.20 or newer.
1. Build Chromium with gtk3 support (use_gtk3=1).
2. Run Chromium with different themes, e.g.:
$ GTK_THEME=Adwaita:dark
3. See white text over white background on address bar.
4. Select some text on a web page, and see white text on white background instead of highlighting.

What is the expected behavior?
Gtk3 theme integration works properly.

What went wrong?
The gtk3 integration is incomplete due to the following things:

1. If the background color cannot be found, it always sets to white color [1], which is bad, especially for dark themes. Maybe it would better to use the background color of the window instead:

gtk_style_context_get_background_color(
      gtk_widget_get_style_context(gtk_widget_get_toplevel(widget)),
      stateMap[state], &color);

2. Since gtk3 version 3.20, the 'label:selected' state is no longer used for background, so querying highlight background color is no longer possible e.g from the Adwaita theme. Instead a new 'selection' CSS node is introduced. [2]

[1] https://chromium.googlesource.com/chromium/src.git/+/master/chrome/browser/ui/libgtk2ui/native_theme_gtk2.cc#141

[2] https://git.gnome.org/browse/gtk+/tree/gtk/theme/Adwaita/gtk-contained.css?h=3.20.6#n113

Did this work before? No 

Chrome version: 52.0.2743.82  Channel: n/a
OS Version: 4.6.4
Flash Version: 

Please complete the gtk3 theme support.