Add initial GTK web accessibility framework (new with valgrind fix).

This is the same as http://codereview.chromium.org/9839069/ which was
landed but reverted due to a valgrind failure in content_unittests.

The valgrind failure was because browser_accessibility_manager_unittest.cc
is constructing its own subclass of BrowserAccessibility (for testing),
but BrowserAccessibilityManagerGtk was assuming that any BrowserAccessibility
could be static_casted to a BrowserAccessibilityGtk. I fixed this by
making ToBrowserAccessibilityGtk() a virtual method with a default impl that
returns NULL.

Original change:

This enables Linux desktop assistive technology such as the Orca screen 
reader to access the web contents. Builds on the same accessibility stack 
used by Mac & Windows already. 

This change works with Orca now, but it's minimal: all that works is getting 
the correct feedback when you tab through focusable links and controls in 
a webpage. Future changes will add the rest of the support. 

BUG=24585
TEST=Run Chrome on desktop Linux with Orca turned on, tab through links. 
TBR=darin,sky
Review URL: https://chromiumcodereview.appspot.com/10381010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@135593 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 37 insertions, 1 deletions

diff --git a/ui/gfx/gtk_preserve_window.cc b/ui/gfx/gtk_preserve_window.cc
index da09570..8ea1c43 100644
--- a/ui/gfx/gtk_preserve_window.cc
+++ b/ui/gfx/gtk_preserve_window.cc
@@ -24,6 +24,10 @@ struct _GtkPreserveWindowPrivate {
   // Whether or not we delegate the resize of the GdkWindow
   // to someone else.
   gboolean delegate_resize;
+
+  // Accessible factory and userdata.
+  AtkObject* (*accessible_factory)(void* userdata);
+  void* accessible_factory_userdata;
 };
 
 G_DEFINE_TYPE(GtkPreserveWindow, gtk_preserve_window, GTK_TYPE_FIXED)
@@ -33,12 +37,14 @@ static void gtk_preserve_window_realize(GtkWidget* widget);
 static void gtk_preserve_window_unrealize(GtkWidget* widget);
 static void gtk_preserve_window_size_allocate(GtkWidget* widget,
                                               GtkAllocation* allocation);
+static AtkObject* gtk_preserve_window_get_accessible(GtkWidget* widget);
 
 static void gtk_preserve_window_class_init(GtkPreserveWindowClass *klass) {
   GtkWidgetClass* widget_class = reinterpret_cast<GtkWidgetClass*>(klass);
   widget_class->realize = gtk_preserve_window_realize;
   widget_class->unrealize = gtk_preserve_window_unrealize;
   widget_class->size_allocate = gtk_preserve_window_size_allocate;
+  widget_class->get_accessible = gtk_preserve_window_get_accessible;
 
   GtkObjectClass* object_class = reinterpret_cast<GtkObjectClass*>(klass);
   object_class->destroy = gtk_preserve_window_destroy;
@@ -50,6 +56,8 @@ static void gtk_preserve_window_class_init(GtkPreserveWindowClass *klass) {
 static void gtk_preserve_window_init(GtkPreserveWindow* widget) {
   GtkPreserveWindowPrivate* priv = GTK_PRESERVE_WINDOW_GET_PRIVATE(widget);
   priv->preserve_window = FALSE;
+  priv->accessible_factory = NULL;
+  priv->accessible_factory_userdata = NULL;
 
   // These widgets always have their own window.
   gtk_widget_set_has_window(GTK_WIDGET(widget), TRUE);
@@ -234,4 +242,23 @@ void gtk_preserve_window_delegate_resize(GtkPreserveWindow* widget,
   priv->delegate_resize = delegate;
 }
 
+void gtk_preserve_window_set_accessible_factory(
+    GtkPreserveWindow* widget,
+    AtkObject* (*factory)(void* userdata),
+    gpointer userdata) {
+  GtkPreserveWindowPrivate* priv = GTK_PRESERVE_WINDOW_GET_PRIVATE(widget);
+  priv->accessible_factory = factory;
+  priv->accessible_factory_userdata = userdata;
+}
+
+AtkObject* gtk_preserve_window_get_accessible(GtkWidget* widget) {
+  GtkPreserveWindowPrivate* priv = GTK_PRESERVE_WINDOW_GET_PRIVATE(widget);
+  if (priv->accessible_factory) {
+    return priv->accessible_factory(priv->accessible_factory_userdata);
+  } else {
+    return GTK_WIDGET_CLASS(gtk_preserve_window_parent_class)
+        ->get_accessible(widget);
+  }
+}
+
 G_END_DECLS
diff --git a/ui/gfx/gtk_preserve_window.h b/ui/gfx/gtk_preserve_window.h
index 37657b3..0af5d7a 100644
--- a/ui/gfx/gtk_preserve_window.h
+++ b/ui/gfx/gtk_preserve_window.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -6,6 +6,7 @@
 #define UI_GFX_GTK_PRESERVE_WINDOW_H_
 #pragma once
 
+#include <atk/atk.h>
 #include <gdk/gdk.h>
 #include <gtk/gtk.h>
 
@@ -61,6 +62,14 @@ void gtk_preserve_window_set_preserve(GtkPreserveWindow* widget,
 UI_EXPORT void gtk_preserve_window_delegate_resize(GtkPreserveWindow* widget,
                                                    gboolean delegate);
 
+// Provide a function to return an AtkObject* when calls to get_accessible
+// are made on this widget. The parameter |userdata| will be passed to the
+// factory function.
+void gtk_preserve_window_set_accessible_factory(
+    GtkPreserveWindow* widget,
+    AtkObject* (*factory)(void* userdata),
+    gpointer userdata);
+
 G_END_DECLS
 
 #endif  // UI_GFX_GTK_PRESERVE_WINDOW_H_