[pitivi] layer: Fix segfault on GTK 3.20

[Alexandru Băluț <alexbalut src gnome org>]

commit 62e5a852f905847e98cc653bc9e06fc8b57ab899
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Sat Apr 16 11:39:19 2016 +0200

    layer: Fix segfault on GTK 3.20
    
    The Layer's do_draw method was not calling EventBox's do_draw method
    and this caused the segfault .. somehow.
    
    Removed the method since it was not doing anything useful.
    
    Fixes https://phabricator.freedesktop.org/T7373
    
    Differential Revision: https://phabricator.freedesktop.org/D912

 pitivi/timeline/layer.py    |    3 ---
 pitivi/timeline/timeline.py |   14 ++++++++------
 2 files changed, 8 insertions(+), 9 deletions(-)
---
diff --git a/pitivi/timeline/layer.py b/pitivi/timeline/layer.py
index f17ebc9..341126a 100644
--- a/pitivi/timeline/layer.py
+++ b/pitivi/timeline/layer.py
@@ -497,6 +497,3 @@ class Layer(Gtk.EventBox, timelineUtils.Zoomable, Loggable):
         for ges_clip in self.ges_layer.get_clips():
             if hasattr(ges_clip, "ui"):
                 ges_clip.ui.updatePosition()
-
-    def do_draw(self, cr):
-        Gtk.Box.do_draw(self, cr)
diff --git a/pitivi/timeline/timeline.py b/pitivi/timeline/timeline.py
index b9d6b45..0b71b75 100644
--- a/pitivi/timeline/timeline.py
+++ b/pitivi/timeline/timeline.py
@@ -246,6 +246,7 @@ class Timeline(Gtk.EventBox, Zoomable, Loggable):
         self.layout.props.can_focus = True
         self.layout.props.can_default = True
         self.__layers_vbox = Gtk.Box(orientation=Gtk.Orientation.VERTICAL)
+        self.__layers_vbox.get_style_context().add_class("LayersBox")
         self.__layers_vbox.props.width_request = self.get_allocated_width()
         self.__layers_vbox.props.height_request = self.get_allocated_height()
         self.layout.put(self.__layers_vbox, 0, 0)
@@ -919,12 +920,13 @@ class Timeline(Gtk.EventBox, Zoomable, Loggable):
         # Check the media types so the controls are set up properly.
         layer.checkMediaTypes()
 
-        layer_widget = Gtk.Box(orientation=Gtk.Orientation.VERTICAL)
-        layer_widget.pack_start(layer.before_sep, False, False, 0)
-        layer_widget.pack_start(layer, True, True, 0)
-        layer_widget.pack_start(layer.after_sep, False, False, 0)
-        layer_widget.show_all()
-        self.__layers_vbox.pack_start(layer_widget, True, True, 0)
+        layer_box = Gtk.Box(orientation=Gtk.Orientation.VERTICAL)
+        layer_box.get_style_context().add_class("LayerBox")
+        layer_box.pack_start(layer.before_sep, False, False, 0)
+        layer_box.pack_start(layer, True, True, 0)
+        layer_box.pack_start(layer.after_sep, False, False, 0)
+        layer_box.show_all()
+        self.__layers_vbox.pack_start(layer_box, True, True, 0)
 
         ges_layer.connect("notify::priority", self.__layerPriorityChangedCb)