[gtk/matthiasc/for-master] migration docs: Updates

[Matthias Clasen <matthiasc src gnome org>]

commit 0d42d65126265e5780dc61b55ff078ecfce1d4aa
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Apr 17 17:50:18 2020 -0400

    migration docs: Updates
    
    Mention shadow type, relief, aspect frame.

 docs/reference/gtk/migrating-3to4.xml | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)
---
diff --git a/docs/reference/gtk/migrating-3to4.xml b/docs/reference/gtk/migrating-3to4.xml
index 65bd1a1443..dab94a146c 100644
--- a/docs/reference/gtk/migrating-3to4.xml
+++ b/docs/reference/gtk/migrating-3to4.xml
@@ -563,6 +563,12 @@
         and always use the context's current state. Update all callers
         to omit the state argument.
       </para>
+      <para>
+        The most commonly used GtkStyleContext API, gtk_style_context_add_class(),
+        has been moved to GtkWidget as gtk_widget_add_css_class(), as have the
+        corresponding gtk_style_context_remove_class() and
+        gtk_style_context_has_class() APIs.
+      </para>
     </section>
 
     <section>
@@ -588,6 +594,17 @@
     </section>
 
     <section>
+      <title>Stop using GtkShadowType and GtkRelief properties</title>
+      <para>
+        The shadow-type properties in GtkScrolledWindow, GtkViewport,
+        and GtkFrame, as well as the relief properties in GtkButton
+        and its subclasses have been removed. GtkScrolledWindow, GtkButton
+        and GtkMenuButton have instead gained a boolean has-frame
+        property.
+      </para>
+    </section>
+
+    <sectionh>
       <title>Adapt to GtkWidget's size request changes</title>
       <para>
         GTK 3 used five different virtual functions in GtkWidget to
@@ -1037,6 +1054,15 @@
       </para>
     </section>
 
+    <section>
+      <title>GtkAspectFrame is no longer a frame</title>
+      <para>
+        GtkAspectFrame is no longer derived from GtkFrame and does not
+        place a label and frame around its child anymore. It still lets
+        you control the aspect ratio of its child.
+      </para>
+    </section>
+
     <section>
       <title>Stop using custom tooltip windows</title>
       <para>