Fix build bustage by removing another dependency on browser/gtk by creating a new TabContentsViewGtk specifically for views. This subclasses WidgetGtk similar to how TabContentsViewWin subclasses WidgetWin.

There was a bug in NativeViewHostGtk - reparenting needs to be done atomically using gtk_widget_reparent since GtkWidgets are refcounted and when removed from a container are released, causing a crash when a TabContents is reparented.

The code now compiles thanks to a stubbed BlockedPopupContainer, however there is one remaining issue - the browser window no longer paints and the app instantly hangs. However this is better than the current state so I figured I'd send the code review.
Review URL: http://codereview.chromium.org/126107

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@18588 0039d316-1c4b-4281-b951-d872f2087c98

6 files changed, 114 insertions, 111 deletions

diff --git a/views/controls/button/native_button_gtk.cc b/views/controls/button/native_button_gtk.cc
index c97d1e0..1680019 100644
--- a/views/controls/button/native_button_gtk.cc
+++ b/views/controls/button/native_button_gtk.cc
@@ -83,7 +83,7 @@ gfx::Size NativeButtonGtk::GetPreferredSize() {
 void NativeButtonGtk::CreateNativeControl() {
   GtkWidget* widget = gtk_button_new();
   g_signal_connect(G_OBJECT(widget), "clicked",
-                   G_CALLBACK(CallClicked), NULL);
+                   G_CALLBACK(CallClicked), this);
   NativeControlCreated(widget);
 }
 
@@ -96,10 +96,8 @@ void NativeButtonGtk::NativeControlCreated(GtkWidget* widget) {
 }
 
 // static
-void NativeButtonGtk::CallClicked(GtkButton* widget) {
-  View* view = NativeViewHostGtk::GetViewForNative(GTK_WIDGET(widget));
-  if (view)
-    static_cast<NativeButtonGtk*>(view)->OnClicked();
+void NativeButtonGtk::CallClicked(GtkButton* widget, NativeButtonGtk* button) {
+  button->OnClicked();
 }
 
 void NativeButtonGtk::OnClicked() {
diff --git a/views/controls/button/native_button_gtk.h b/views/controls/button/native_button_gtk.h
index e719202..6c3f600 100644
--- a/views/controls/button/native_button_gtk.h
+++ b/views/controls/button/native_button_gtk.h
@@ -36,7 +36,7 @@ class NativeButtonGtk : public NativeControlGtk, public NativeButtonWrapper {
   virtual bool IsCheckbox() const { return false; }
 
  private:
-  static void CallClicked(GtkButton* widget);
+  static void CallClicked(GtkButton* widget, NativeButtonGtk* button);
 
   // Invoked when the user clicks on the button.
   void OnClicked();
diff --git a/views/controls/native/native_view_host_gtk.cc b/views/controls/native/native_view_host_gtk.cc
index 7f59144..6fa7325 100644
--- a/views/controls/native/native_view_host_gtk.cc
+++ b/views/controls/native/native_view_host_gtk.cc
@@ -24,47 +24,21 @@ NativeViewHostGtk::NativeViewHostGtk(NativeViewHost* host)
 NativeViewHostGtk::~NativeViewHostGtk() {
 }
 
-// static
-View* NativeViewHostGtk::GetViewForNative(GtkWidget* widget) {
-  gpointer user_data = g_object_get_data(G_OBJECT(widget), "chrome-view");
-  return static_cast<View*>(user_data);
-}
-
-// static
-void NativeViewHostGtk::SetViewForNative(GtkWidget* widget, View* view) {
-  g_object_set_data(G_OBJECT(widget), "chrome-view", view);
-}
-
 ////////////////////////////////////////////////////////////////////////////////
 // NativeViewHostGtk, NativeViewHostWrapper implementation:
 
 void NativeViewHostGtk::NativeViewAttached() {
   DCHECK(host_->native_view());
 
-  GtkWidget* current_parent = gtk_widget_get_parent(host_->native_view());
-  GtkWidget* new_parent = host_->GetWidget()->GetNativeView();
-  // Only adjust the parent if the parent actually changed.
-  if (current_parent != new_parent) {
-    // First hide the new window. We don't want anything to draw (like sub-hwnd
-    // borders), when we change the parent below.
-    gtk_widget_hide(host_->native_view());
-
-    if (current_parent) {
-      gtk_container_remove(GTK_CONTAINER(current_parent),
-                           host_->native_view());
-    }
-
-    // Adds a mapping between the GtkWidget and us.
-    SetViewForNative(host_->native_view(), host_);
-
-    if (!destroy_signal_id_) {
-      destroy_signal_id_ = g_signal_connect(G_OBJECT(host_->native_view()),
-                                            "destroy", G_CALLBACK(CallDestroy),
-                                            NULL);
-    }
+  if (gtk_widget_get_parent(host_->native_view()))
+    GetHostWidget()->ReparentChild(host_->native_view());
+  else
+    GetHostWidget()->AddChild(host_->native_view());
 
-    // Set the parent.
-    static_cast<WidgetGtk*>(host_->GetWidget())->AddChild(host_->native_view());
+  if (!destroy_signal_id_) {
+    destroy_signal_id_ = g_signal_connect(G_OBJECT(host_->native_view()),
+                                          "destroy", G_CALLBACK(CallDestroy),
+                                          this);
   }
 
   // Always layout though.
@@ -88,9 +62,9 @@ void NativeViewHostGtk::NativeViewDetaching() {
 void NativeViewHostGtk::AddedToWidget() {
   if (!host_->native_view())
     return;
-  WidgetGtk* parent_widget = static_cast<WidgetGtk*>(host_->GetWidget());
+  WidgetGtk* parent_widget = GetHostWidget();
   GtkWidget* widget_parent = gtk_widget_get_parent(host_->native_view());
-  GtkWidget* parent_widget_widget = parent_widget->child_widget_parent();
+  GtkWidget* parent_widget_widget = parent_widget->window_contents();
   if (widget_parent != parent_widget_widget) {
     g_object_ref(host_->native_view());
     if (widget_parent)
@@ -110,10 +84,10 @@ void NativeViewHostGtk::RemovedFromWidget() {
   if (!host_->native_view())
     return;
 
-  WidgetGtk* parent_widget = static_cast<WidgetGtk*>(host_->GetWidget());
+  WidgetGtk* parent_widget = GetHostWidget();
   gtk_widget_hide(host_->native_view());
   if (parent_widget) {
-    gtk_container_remove(GTK_CONTAINER(parent_widget->child_widget_parent()),
+    gtk_container_remove(GTK_CONTAINER(parent_widget->window_contents()),
                          host_->native_view());
   }
 }
@@ -157,8 +131,7 @@ void NativeViewHostGtk::UninstallClip() {
 }
 
 void NativeViewHostGtk::ShowWidget(int x, int y, int w, int h) {
-  WidgetGtk* parent = static_cast<WidgetGtk*>(host_->GetWidget());
-  parent->PositionChild(host_->native_view(), x, y, w, h);
+  GetHostWidget()->PositionChild(host_->native_view(), x, y, w, h);
   gtk_widget_show(host_->native_view());
 }
 
@@ -173,13 +146,14 @@ void NativeViewHostGtk::SetFocus() {
 ////////////////////////////////////////////////////////////////////////////////
 // NativeViewHostGtk, private:
 
-// static
-void NativeViewHostGtk::CallDestroy(GtkObject* object) {
-  View* view = GetViewForNative(GTK_WIDGET(object));
-  if (!view)
-    return;
+WidgetGtk* NativeViewHostGtk::GetHostWidget() const {
+  return static_cast<WidgetGtk*>(host_->GetWidget());
+}
 
-  return static_cast<NativeViewHost*>(view)->NativeViewDestroyed();
+// static
+void NativeViewHostGtk::CallDestroy(GtkObject* object,
+                                    NativeViewHostGtk* host) {
+  return host->host_->NativeViewDestroyed();
 }
 
 ////////////////////////////////////////////////////////////////////////////////
diff --git a/views/controls/native/native_view_host_gtk.h b/views/controls/native/native_view_host_gtk.h
index 40a6a65..154da70 100644
--- a/views/controls/native/native_view_host_gtk.h
+++ b/views/controls/native/native_view_host_gtk.h
@@ -14,17 +14,13 @@
 namespace views {
 
 class View;
+class WidgetGtk;
 
 class NativeViewHostGtk : public NativeViewHostWrapper {
  public:
   explicit NativeViewHostGtk(NativeViewHost* host);
   virtual ~NativeViewHostGtk();
 
-  // Sets and retrieves the View associated with a particular widget.
-  // TODO(beng): move to NativeViewHost, and have take gfx::NativeViews.
-  static View* GetViewForNative(GtkWidget* widget);
-  static void SetViewForNative(GtkWidget* widget, View* view);
-
   // Overridden from NativeViewHostWrapper:
   virtual void NativeViewAttached();
   virtual void NativeViewDetaching();
@@ -38,6 +34,11 @@ class NativeViewHostGtk : public NativeViewHostWrapper {
   virtual void SetFocus();
 
  private:
+  WidgetGtk* GetHostWidget() const;
+
+  // Invoked from the 'destroy' signal.
+  static void CallDestroy(GtkObject* object, NativeViewHostGtk* host);
+
   // Our associated NativeViewHost.
   NativeViewHost* host_;
 
@@ -48,9 +49,6 @@ class NativeViewHostGtk : public NativeViewHostWrapper {
   // Signal handle id for 'destroy' signal.
   gulong destroy_signal_id_;
 
-  // Invoked from the 'destroy' signal.
-  static void CallDestroy(GtkObject* object);
-
   DISALLOW_COPY_AND_ASSIGN(NativeViewHostGtk);
 };
 
diff --git a/views/widget/widget_gtk.cc b/views/widget/widget_gtk.cc
index 7d7e74b..1aec6a4 100644
--- a/views/widget/widget_gtk.cc
+++ b/views/widget/widget_gtk.cc
@@ -53,6 +53,9 @@ static int GetFlagsForEventButton(const GdkEventButton& event) {
   return flags;
 }
 
+// static
+GtkWidget* WidgetGtk::null_parent_ = NULL;
+
 ////////////////////////////////////////////////////////////////////////////////
 // WidgetGtk, public:
 
@@ -60,7 +63,7 @@ WidgetGtk::WidgetGtk(Type type)
     : is_window_(false),
       type_(type),
       widget_(NULL),
-      child_widget_parent_(NULL),
+      window_contents_(NULL),
       is_mouse_down_(false),
       has_capture_(false),
       last_mouse_event_was_move_(false),
@@ -84,7 +87,7 @@ void WidgetGtk::Init(GtkWidget* parent,
 #endif
 
   // Make container here.
-  CreateGtkWidget();
+  CreateGtkWidget(parent);
 
   // Make sure we receive our motion events.
 
@@ -92,7 +95,7 @@ void WidgetGtk::Init(GtkWidget* parent,
   // minimum we need painting to happen on the parent (otherwise painting
   // doesn't work at all), and similarly we need mouse release events on the
   // parent as windows don't get mouse releases.
-  gtk_widget_add_events(child_widget_parent_,
+  gtk_widget_add_events(window_contents_,
                         GDK_ENTER_NOTIFY_MASK |
                         GDK_LEAVE_NOTIFY_MASK |
                         GDK_BUTTON_PRESS_MASK |
@@ -109,33 +112,34 @@ void WidgetGtk::Init(GtkWidget* parent,
 
   MessageLoopForUI::current()->AddObserver(this);
 
-  g_signal_connect_after(G_OBJECT(child_widget_parent_), "size_allocate",
+  // TODO(beng): make these take this rather than NULL.
+  g_signal_connect_after(G_OBJECT(window_contents_), "size_allocate",
                          G_CALLBACK(CallSizeAllocate), NULL);
-  g_signal_connect(G_OBJECT(child_widget_parent_), "expose_event",
+  g_signal_connect(G_OBJECT(window_contents_), "expose_event",
                    G_CALLBACK(CallPaint), NULL);
-  g_signal_connect(G_OBJECT(child_widget_parent_), "enter_notify_event",
+  g_signal_connect(G_OBJECT(window_contents_), "enter_notify_event",
                    G_CALLBACK(CallEnterNotify), NULL);
-  g_signal_connect(G_OBJECT(child_widget_parent_), "leave_notify_event",
+  g_signal_connect(G_OBJECT(window_contents_), "leave_notify_event",
                    G_CALLBACK(CallLeaveNotify), NULL);
-  g_signal_connect(G_OBJECT(child_widget_parent_), "motion_notify_event",
+  g_signal_connect(G_OBJECT(window_contents_), "motion_notify_event",
                    G_CALLBACK(CallMotionNotify), NULL);
-  g_signal_connect(G_OBJECT(child_widget_parent_), "button_press_event",
+  g_signal_connect(G_OBJECT(window_contents_), "button_press_event",
                    G_CALLBACK(CallButtonPress), NULL);
-  g_signal_connect(G_OBJECT(child_widget_parent_), "button_release_event",
+  g_signal_connect(G_OBJECT(window_contents_), "button_release_event",
                    G_CALLBACK(CallButtonRelease), NULL);
-  g_signal_connect(G_OBJECT(child_widget_parent_), "grab_broken_event",
+  g_signal_connect(G_OBJECT(window_contents_), "focus_out_event",
+                   G_CALLBACK(CallFocusOut), NULL);
+  g_signal_connect(G_OBJECT(window_contents_), "grab_broken_event",
                    G_CALLBACK(CallGrabBrokeEvent), NULL);
-  g_signal_connect(G_OBJECT(child_widget_parent_), "grab_notify",
+  g_signal_connect(G_OBJECT(window_contents_), "grab_notify",
                    G_CALLBACK(CallGrabNotify), NULL);
-  g_signal_connect(G_OBJECT(child_widget_parent_), "focus_out_event",
-                   G_CALLBACK(CallFocusOut), NULL);
-  g_signal_connect(G_OBJECT(child_widget_parent_), "key_press_event",
+  g_signal_connect(G_OBJECT(window_contents_), "key_press_event",
                    G_CALLBACK(CallKeyPress), NULL);
-  g_signal_connect(G_OBJECT(child_widget_parent_), "key_release_event",
+  g_signal_connect(G_OBJECT(window_contents_), "key_release_event",
                    G_CALLBACK(CallKeyRelease), NULL);
-  g_signal_connect(G_OBJECT(child_widget_parent_), "scroll_event",
+  g_signal_connect(G_OBJECT(window_contents_), "scroll_event",
                    G_CALLBACK(CallScroll), NULL);
-  g_signal_connect(G_OBJECT(child_widget_parent_), "visibility_notify_event",
+  g_signal_connect(G_OBJECT(window_contents_), "visibility_notify_event",
                    G_CALLBACK(CallVisibilityNotify), NULL);
 
   // In order to receive notification when the window is no longer the front
@@ -167,10 +171,12 @@ void WidgetGtk::Init(GtkWidget* parent,
   tooltip_manager_.reset(new TooltipManagerGtk(this));
 
   if (type_ == TYPE_CHILD) {
-    WidgetGtk* parent_widget = GetViewForNative(parent);
-    parent_widget->AddChild(widget_);
-    parent_widget->PositionChild(widget_, bounds.x(), bounds.y(),
-                                 bounds.width(), bounds.height());
+    if (parent) {
+      WidgetGtk* parent_widget = GetViewForNative(parent);
+      parent_widget->AddChild(widget_);
+      parent_widget->PositionChild(widget_, bounds.x(), bounds.y(),
+                                   bounds.width(), bounds.height());
+    }
   } else {
     if (bounds.width() > 0 && bounds.height() > 0)
       gtk_window_resize(GTK_WINDOW(widget_), bounds.width(), bounds.height());
@@ -199,11 +205,15 @@ bool WidgetGtk::MakeTransparent() {
 }
 
 void WidgetGtk::AddChild(GtkWidget* child) {
-  gtk_container_add(GTK_CONTAINER(child_widget_parent_), child);
+  gtk_container_add(GTK_CONTAINER(window_contents_), child);
 }
 
 void WidgetGtk::RemoveChild(GtkWidget* child) {
-  gtk_container_remove(GTK_CONTAINER(child_widget_parent_), child);
+  gtk_container_remove(GTK_CONTAINER(window_contents_), child);
+}
+
+void WidgetGtk::ReparentChild(GtkWidget* child) {
+  gtk_widget_reparent(child, window_contents_);
 }
 
 void WidgetGtk::PositionChild(GtkWidget* child, int x, int y, int w, int h) {
@@ -211,7 +221,7 @@ void WidgetGtk::PositionChild(GtkWidget* child, int x, int y, int w, int h) {
   // For some reason we need to do both of these to size a widget.
   gtk_widget_size_allocate(child, &alloc);
   gtk_widget_set_size_request(child, w, h);
-  gtk_fixed_move(GTK_FIXED(child_widget_parent_), child, x, y);
+  gtk_fixed_move(GTK_FIXED(window_contents_), child, x, y);
 }
 
 void WidgetGtk::SetContentsView(View* view) {
@@ -389,10 +399,17 @@ void WidgetGtk::DidProcessEvent(GdkEvent* event) {
 ////////////////////////////////////////////////////////////////////////////////
 // TODO(beng): organize into sections:
 
-void WidgetGtk::CreateGtkWidget() {
+void WidgetGtk::CreateGtkWidget(GtkWidget* parent) {
   if (type_ == TYPE_CHILD) {
-    child_widget_parent_ = widget_ = gtk_fixed_new();
+    window_contents_ = widget_ = gtk_fixed_new();
     gtk_fixed_set_has_window(GTK_FIXED(widget_), true);
+    if (!parent && !null_parent_) {
+      GtkWidget* popup = gtk_window_new(GTK_WINDOW_POPUP);
+      null_parent_ = gtk_fixed_new();
+      gtk_container_add(GTK_CONTAINER(popup), null_parent_);
+      gtk_widget_realize(null_parent_);
+    }
+    gtk_container_add(GTK_CONTAINER(parent ? parent : null_parent_), widget_);
     SetViewForNative(widget_, this);
   } else {
     widget_ = gtk_window_new(
@@ -403,16 +420,15 @@ void WidgetGtk::CreateGtkWidget() {
     SetWindowForNative(widget_, static_cast<WindowGtk*>(this));
     SetViewForNative(widget_, this);
 
-    child_widget_parent_ = gtk_fixed_new();
-    gtk_fixed_set_has_window(GTK_FIXED(child_widget_parent_), true);
-    gtk_container_add(GTK_CONTAINER(widget_), child_widget_parent_);
-    gtk_widget_show(child_widget_parent_);
-    SetViewForNative(child_widget_parent_, this);
+    window_contents_ = gtk_fixed_new();
+    gtk_fixed_set_has_window(GTK_FIXED(window_contents_), true);
+    gtk_container_add(GTK_CONTAINER(widget_), window_contents_);
+    gtk_widget_show(window_contents_);
+    SetViewForNative(window_contents_, this);
 
     if (transparent_)
       ConfigureWidgetForTransparentBackground();
   }
-
   // The widget needs to be realized before handlers like size-allocate can
   // function properly.
   gtk_widget_realize(widget_);
@@ -500,12 +516,12 @@ gboolean WidgetGtk::OnGrabBrokeEvent(GtkWidget* widget, GdkEvent* event) {
 }
 
 void WidgetGtk::OnGrabNotify(GtkWidget* widget, gboolean was_grabbed) {
-  gtk_grab_remove(child_widget_parent_);
+  gtk_grab_remove(window_contents_);
   HandleGrabBroke();
 }
 
 void WidgetGtk::OnDestroy(GtkWidget* widget) {
-  widget_ = child_widget_parent_ = NULL;
+  widget_ = window_contents_ = NULL;
   root_view_->OnWidgetDestroyed();
   if (delete_on_destroy_)
     delete this;
@@ -564,7 +580,7 @@ bool WidgetGtk::ProcessMousePressed(GdkEventButton* event) {
     is_mouse_down_ = true;
     if (!has_capture_) {
       has_capture_ = true;
-      gtk_grab_add(child_widget_parent_);
+      gtk_grab_add(window_contents_);
     }
     return true;
   }
@@ -581,7 +597,7 @@ void WidgetGtk::ProcessMouseReleased(GdkEventButton* event) {
 
   if (has_capture_ && ReleaseCaptureOnMouseReleased()) {
     has_capture_ = false;
-    gtk_grab_remove(child_widget_parent_);
+    gtk_grab_remove(window_contents_);
   }
   is_mouse_down_ = false;
   root_view_->OnMouseReleased(mouse_up, false);
@@ -763,8 +779,7 @@ Window* WidgetGtk::GetWindowImpl(GtkWidget* widget) {
 }
 
 void WidgetGtk::ConfigureWidgetForTransparentBackground() {
-  DCHECK(widget_ && child_widget_parent_ &&
-         widget_ != child_widget_parent_);
+  DCHECK(widget_ && window_contents_ && widget_ != window_contents_);
 
   GdkColormap* rgba_colormap =
       gdk_screen_get_rgba_colormap(gdk_screen_get_default());
@@ -785,12 +800,12 @@ void WidgetGtk::ConfigureWidgetForTransparentBackground() {
   // Widget must be realized before setting pixmap.
   gdk_window_set_back_pixmap(widget_->window, NULL, FALSE);
 
-  gtk_widget_set_colormap(child_widget_parent_, rgba_colormap);
-  gtk_widget_set_app_paintable(child_widget_parent_, true);
-  GTK_WIDGET_UNSET_FLAGS(child_widget_parent_, GTK_DOUBLE_BUFFERED);
-  gtk_widget_realize(child_widget_parent_);
+  gtk_widget_set_colormap(window_contents_, rgba_colormap);
+  gtk_widget_set_app_paintable(window_contents_, true);
+  GTK_WIDGET_UNSET_FLAGS(window_contents_, GTK_DOUBLE_BUFFERED);
+  gtk_widget_realize(window_contents_);
   // Widget must be realized before setting pixmap.
-  gdk_window_set_back_pixmap(child_widget_parent_->window, NULL, FALSE);
+  gdk_window_set_back_pixmap(window_contents_->window, NULL, FALSE);
 }
 
 void WidgetGtk::HandleGrabBroke() {
diff --git a/views/widget/widget_gtk.h b/views/widget/widget_gtk.h
index 2442f74..b5dd6a0 100644
--- a/views/widget/widget_gtk.h
+++ b/views/widget/widget_gtk.h
@@ -56,15 +56,25 @@ class WidgetGtk : public Widget, public MessageLoopForUI::Observer {
     delete_on_destroy_ = delete_on_destroy;
   }
 
+  // Adds and removes the specified widget as a child of this widget's contents.
+  // These methods make sure to add the widget to the window's contents
+  // container if this widget is a window.
   void AddChild(GtkWidget* child);
   void RemoveChild(GtkWidget* child);
 
+  // A safe way to reparent a child widget to this widget. Calls
+  // gtk_widget_reparent which handles refcounting to avoid destroying the
+  // widget when removing it from its old parent.
+  void ReparentChild(GtkWidget* child);
+
   // Positions a child GtkWidget at the specified location and bounds.
   void PositionChild(GtkWidget* child, int x, int y, int w, int h);
 
-  // Parent GtkWidget all children are added to. This is not necessarily
-  // the same as returned by GetNativeView.
-  GtkWidget* child_widget_parent() const { return child_widget_parent_; }
+  // Parent GtkWidget all children are added to. When this WidgetGtk corresponds
+  // to a top level window, this is the GtkFixed within the GtkWindow, not the
+  // GtkWindow itself. For child widgets, this is the same GtkFixed as
+  // |widget_|.
+  GtkWidget* window_contents() const { return window_contents_; }
 
   virtual void SetContentsView(View* view);
 
@@ -174,7 +184,10 @@ class WidgetGtk : public Widget, public MessageLoopForUI::Observer {
   static Window* GetWindowImpl(GtkWidget* widget);
 
   // Creates the GtkWidget.
-  void CreateGtkWidget();
+  void CreateGtkWidget(GtkWidget* parent);
+
+  // Attaches the widget contents to the window's widget.
+  void AttachGtkWidgetToWindow();
 
   // Invoked from create widget to enable the various bits needed for a
   // transparent background. This is only invoked if MakeTransparent has been
@@ -186,10 +199,15 @@ class WidgetGtk : public Widget, public MessageLoopForUI::Observer {
   const Type type_;
 
   // Our native views. If we're a window/popup, then widget_ is the window and
-  // child_widget_parent_ is a GtkFixed. If we're not a window/popup, then
-  // widget_ and child_widget_parent_ are a GtkFixed.
+  // window_contents_ is a GtkFixed. If we're not a window/popup, then widget_
+  // and window_contents_ point to the same GtkFixed.
   GtkWidget* widget_;
-  GtkWidget* child_widget_parent_;
+  GtkWidget* window_contents_;
+
+  // Child GtkWidgets created with no parent need to be parented to a valid top
+  // level window otherwise Gtk throws a fit. |null_parent_| is an invisible
+  // popup that such GtkWidgets are parented to.
+  static GtkWidget* null_parent_;
 
   // The root of the View hierarchy attached to this window.
   scoped_ptr<RootView> root_view_;