GTK: Speculative fix for crash in BalloonViewHost.

chrome/browser/ui/gtk/notifications/balloon_view_host_gtk.cc

 // Copyright (c) 2011 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.
 
 #include "chrome/browser/ui/gtk/notifications/balloon_view_host_gtk.h"
 
 #include "chrome/browser/notifications/balloon.h"
 #include "content/browser/renderer_host/render_view_host.h"
 #include "content/browser/renderer_host/render_widget_host_view_gtk.h"
 #include "content/browser/tab_contents/tab_contents.h"
 
 BalloonViewHost::BalloonViewHost(Balloon* balloon)
     : BalloonHost(balloon) {
 }
 
 BalloonViewHost::~BalloonViewHost() {
   Shutdown();
 }
 
 void BalloonViewHost::UpdateActualSize(const gfx::Size& new_size) {
-  tab_contents_->render_view_host()->view()->SetSize(new_size);
+  RenderViewHost* host = tab_contents_->render_view_host();
+  if (host) {
+    RenderWidgetHostView* view = host->view();
+    if (view)
+      view->SetSize(new_size);
+  }
+
   gtk_widget_set_size_request(
       native_view(), new_size.width(), new_size.height());
 }
 
 gfx::NativeView BalloonViewHost::native_view() const {
   return tab_contents_->GetNativeView();
 }