[gtk+] Add a FLAT style class

[Matthias Clasen <matthiasc src gnome org>]

commit e6341a0b630635438982b9abe9c02d48041a1bc0
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu Jun 26 22:00:29 2014 -0400

    Add a FLAT style class
    
    This will be used for frame-less buttons and frames in the future.

 docs/reference/gtk/gtk3-sections.txt |    1 +
 gtk/gtkstylecontext.h                |   11 +++++++++++
 2 files changed, 12 insertions(+), 0 deletions(-)
---
diff --git a/docs/reference/gtk/gtk3-sections.txt b/docs/reference/gtk/gtk3-sections.txt
index 5896a79..f32a782 100644
--- a/docs/reference/gtk/gtk3-sections.txt
+++ b/docs/reference/gtk/gtk3-sections.txt
@@ -5977,6 +5977,7 @@ GTK_STYLE_CLASS_ENTRY
 GTK_STYLE_CLASS_ERROR
 GTK_STYLE_CLASS_EXPANDER
 GTK_STYLE_CLASS_FRAME
+GTK_STYLE_CLASS_FLAT
 GTK_STYLE_CLASS_GRIP
 GTK_STYLE_CLASS_HEADER
 GTK_STYLE_CLASS_HIGHLIGHT
diff --git a/gtk/gtkstylecontext.h b/gtk/gtkstylecontext.h
index 22182b3..d141476 100644
--- a/gtk/gtkstylecontext.h
+++ b/gtk/gtkstylecontext.h
@@ -826,6 +826,17 @@ struct _GtkStyleContextClass
 #define GTK_STYLE_CLASS_MESSAGE_DIALOG "message-dialog"
 
 /**
+ * GTK_STYLE_CLASS_FLAT:
+ *
+ * A CSS class that is added when widgets that usually have
+ * a frame or border (like buttons or entries) should appear
+ * without it.
+ *
+ * Since: 3.14
+ */
+#define GTK_STYLE_CLASS_FLAT "flat"
+
+/**
  * GTK_STYLE_REGION_ROW:
  *
  * A widget region name to define a treeview row.