Gdk: add an experimental backend for mir

This is disabled by default.  Enable with --enable-mir-backend.

This backend is a combined work of Robert Ancell and Ryan Lortie.

docs/reference/gtk/Makefile.am

@@ -146,6 +146,7 @@ content_files =					\
 	osx.sgml				\
 	broadway.xml				\
 	wayland.xml				\
+	mir.xml					\
 	question_index.sgml			\
 	resources.sgml				\
 	text_widget.sgml			\

docs/reference/gtk/building.sgml

@@ -407,6 +407,11 @@ How to compile GTK+ itself
             <arg choice="plain">--disable-wayland-backend</arg>
           </group>
           <sbr/>
+          <group>
+            <arg choice="plain">--enable-mir-backend</arg>
+            <arg choice="plain">--disable-mir-backend</arg>
+          </group>
+          <sbr/>
           <group>
             <arg choice="plain">--enable-introspection=[no/auto/yes]</arg>
           </group>
@@ -608,8 +613,10 @@ How to compile GTK+ itself
           <systemitem>--disable-quartz-backend</systemitem>,
           <systemitem>--enable-broadway-backend</systemitem>,
           <systemitem>--disable-broadway-backend</systemitem>,
-          <systemitem>--enable-wayland-backend</systemitem>, and
-          <systemitem>--disable-wayland-backend</systemitem></title>
+          <systemitem>--enable-wayland-backend</systemitem>,
+          <systemitem>--disable-wayland-backend</systemitem>
+          <systemitem>--enable-mir-backend</systemitem>, and
+          <systemitem>--disable-mir-backend</systemitem></title>
 
         <para>
           Enables specific backends for GDK.  If none of these options

docs/reference/gtk/gtk-docs.sgml

@@ -416,6 +416,7 @@
     <xi:include href="osx.sgml" />
     <xi:include href="broadway.xml" />
     <xi:include href="wayland.xml" />
+    <xi:include href="mir.xml" />
   </part>
 
   <xi:include href="glossary.xml" />

docs/reference/gtk/mir.xml

@@ -0,0 +1,35 @@
+<?xml version="1.0"?>
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
+               "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
+]>
+<refentry id="gtk-mir">
+<refmeta>
+<refentrytitle>Using GTK+ with Mir</refentrytitle>
+<manvolnum>3</manvolnum>
+<refmiscinfo>GTK Library</refmiscinfo>
+</refmeta>
+
+<refnamediv>
+<refname>Using GTK+ with Mir</refname>
+<refpurpose>
+Mir-specific aspects of using GTK+
+</refpurpose>
+</refnamediv>
+
+<refsect1>
+<title>Using GTK+ with Mir</title>
+
+<para>
+The GDK Mir backend provides support for running GTK+ applications
+under Mir based display servers. To run your application in this way,
+select the Mir backend by setting <literal>GDK_BACKEND=mir</literal>.
+</para>
+
+<para>
+Currently, the Mir backend does not use any additional commandline
+options or environment variables.
+</para>
+
+</refsect1>
+
+</refentry>

docs/reference/gtk/running.sgml

@@ -491,6 +491,11 @@ nevertheless.
         <listitem><para>Selects the Wayland backend for connecting to Wayland display servers</para></listitem>
       </varlistentry>
 
+      <varlistentry>
+        <term>mir</term>
+        <listitem><para>Selects the Mir backend for connecting to Mir display servers</para></listitem>
+      </varlistentry>
+
     </variablelist>
     Since 3.10, this environment variable can contain a comma-separated list
     of backend names, which are tried in order. The list may also contain