aura: Ensure OwnedMailbox not used with invalid or destroyed GLHelper.

content/browser/aura/owned_mailbox.cc

 // Copyright 2013 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 "content/browser/aura/owned_mailbox.h"
 
 #include "base/logging.h"
 #include "content/browser/aura/image_transport_factory.h"
 #include "content/common/gpu/client/gl_helper.h"
 
 namespace content {
 
 OwnedMailbox::OwnedMailbox(GLHelper* gl_helper)
     : texture_id_(0), sync_point_(0), gl_helper_(gl_helper) {
   texture_id_ = gl_helper_->CreateTexture();
   mailbox_ = gl_helper_->ProduceMailboxFromTexture(texture_id_, &sync_point_);
   ImageTransportFactory::GetInstance()->AddObserver(this);
 }
 
 OwnedMailbox::~OwnedMailbox() {
-  ImageTransportFactory::GetInstance()->RemoveObserver(this);
-  if (gl_helper_) {
-    gl_helper_->WaitSyncPoint(sync_point_);
-    gl_helper_->DeleteTexture(texture_id_);
-  }
+  if (gl_helper_)
+    Destroy();
 }
 
 void OwnedMailbox::UpdateSyncPoint(uint32 sync_point) {
   if (sync_point)
     sync_point_ = sync_point;
 }
 
-void OwnedMailbox::OnLostResources() {
+void OwnedMailbox::Destroy() {
+  ImageTransportFactory::GetInstance()->RemoveObserver(this);
   gl_helper_->WaitSyncPoint(sync_point_);
   gl_helper_->DeleteTexture(texture_id_);
   texture_id_ = 0;
   mailbox_ = gpu::Mailbox();
   sync_point_ = 0;
   gl_helper_ = NULL;
 }
 
+void OwnedMailbox::OnLostResources() {
+  if (gl_helper_)
+    Destroy();
+}
+
 }  // namespace content