Add GtkNativeDialog abstract base class

This is a base class that essentially mirrors GtkDialog, but
it is not a GtkWindow, as the actual implemetation will be using
native code.

The base class has show and hide vfuncs, as well as a helper function
to run the dialog in a modal fashion.

This will be later used by the native file chooser dialog.

docs/reference/gtk/gtk-docs.sgml

@@ -203,6 +203,7 @@
       <xi:include href="xml/gtkcolorchooserdialog.xml" />
       <xi:include href="xml/gtkfilechooser.xml" />
       <xi:include href="xml/gtkfilechooserbutton.xml" />
+      <xi:include href="xml/gtknativedialog.xml" />
       <xi:include href="xml/gtkfilechooserdialog.xml" />
       <xi:include href="xml/gtkfilechooserwidget.xml" />
       <xi:include href="xml/gtkfilefilter.xml" />

docs/reference/gtk/gtk3-sections.txt

@@ -2493,6 +2493,27 @@ GtkMiscPrivate
 gtk_misc_get_type
 </SECTION>
 
+<SECTION>
+<FILE>gtknativedialog</FILE>
+<TITLE>GtkNativeDialog</TITLE>
+GTK_TYPE_NATIVE_DIALOG
+GtkNativeDialogClass
+gtk_native_dialog_show
+gtk_native_dialog_hide
+gtk_native_dialog_get_visible
+gtk_native_dialog_set_modal
+gtk_native_dialog_get_modal
+gtk_native_dialog_set_title
+gtk_native_dialog_get_title
+gtk_native_dialog_set_transient_for
+gtk_native_dialog_get_transient_for
+gtk_native_dialog_run
+<SUBSECTION Standard>
+GtkNativeDialog
+<SUBSECTION Private>
+gtk_native_dialog_get_type
+</SECTION>
+
 <SECTION>
 <FILE>gtknotebook</FILE>
 <TITLE>GtkNotebook</TITLE>

gtk/Makefile.am

@@ -229,6 +229,7 @@ gtk_public_h_sources = 		\
 	gtkmodelbutton.h	\
 	gtkmodules.h		\
 	gtkmountoperation.h	\
+	gtknativedialog.h	\
 	gtknotebook.h		\
 	gtkoffscreenwindow.h	\
 	gtkorientable.h		\
@@ -481,6 +482,7 @@ gtk_private_h_sources =		\
 	gtkmodifierstyle.h	\
 	gtkmodulesprivate.h	\
 	gtkmountoperationprivate.h \
+	gtknativedialogprivate.h \
 	gtkorientableprivate.h	\
 	gtkpango.h		\
 	gtkpathbar.h		\
@@ -760,6 +762,7 @@ gtk_base_c_sources = 		\
 	gtkmodifierstyle.c	\
 	gtkmodules.c		\
 	gtkmountoperation.c	\
+	gtknativedialog.c	\
 	gtknotebook.c		\
 	gtkoffscreenwindow.c	\
 	gtkorientable.c		\

gtk/gtk.h

@@ -144,6 +144,7 @@
 #include <gtk/gtkmodelbutton.h>
 #include <gtk/gtkmodules.h>
 #include <gtk/gtkmountoperation.h>
+#include <gtk/gtknativedialog.h>
 #include <gtk/gtknotebook.h>
 #include <gtk/gtkoffscreenwindow.h>
 #include <gtk/gtkorientable.h>