Unbind video texture from mailbox after copying to WebGL.

gpu/command_buffer/service/mailbox_manager_sync.cc

 // Copyright 2014 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 "gpu/command_buffer/service/mailbox_manager_sync.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <queue>
@@ skipping 221 matching lines @@
       // The texture is already known under this name.
       return;
     }
   }
 
   if (group_for_mailbox) {
     // Unlink the mailbox from its current group.
     group_for_mailbox->RemoveName(mailbox);
   }
 
+  if (!texture)
+    return;
+
   if (group_for_texture) {
     group_for_texture->AddName(mailbox);
   } else {
     // This is a new texture, so create a new group.
     texture->SetMailboxManager(this);
     TextureDefinition definition;
     if (!SkipTextureWorkarounds(texture)) {
       base::AutoUnlock unlock(g_lock.Get());
       definition = TextureDefinition(texture, kNewTextureVersion, NULL);
     }
@@ skipping 80 matching lines @@
 
   if (!needs_update.empty()) {
     for (const TextureUpdatePair& pair : needs_update) {
       pair.second.UpdateTexture(pair.first);
     }
   }
 }
 
 }  // namespace gles2
 }  // namespace gpu