Clean up some old TODOs

chrome/renderer/renderer_webidbtransaction_impl.cc

 // Copyright (c) 2010 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/renderer/renderer_webidbtransaction_impl.h"
 
 #include "chrome/common/indexed_db_messages.h"
 #include "chrome/renderer/indexed_db_dispatcher.h"
 #include "chrome/renderer/render_thread.h"
 #include "chrome/renderer/renderer_webidbobjectstore_impl.h"
 #include "third_party/WebKit/WebKit/chromium/public/WebIDBObjectStore.h"
 #include "third_party/WebKit/WebKit/chromium/public/WebIDBTransactionCallbacks.h"
 #include "third_party/WebKit/WebKit/chromium/public/WebString.h"
 
 using WebKit::WebIDBObjectStore;
 using WebKit::WebIDBTransactionCallbacks;
 using WebKit::WebString;
 
 RendererWebIDBTransactionImpl::RendererWebIDBTransactionImpl(
     int32 idb_transaction_id)
     : idb_transaction_id_(idb_transaction_id) {
 }
 
 RendererWebIDBTransactionImpl::~RendererWebIDBTransactionImpl() {
+  // It's not possible for there to be pending callbacks that address this
+  // object since inside WebKit, they hold a reference to the object wich owns
+  // this object. But, if that ever changed, then we'd need to invalidate
+  // any such pointers.
   RenderThread::current()->Send(new IndexedDBHostMsg_TransactionDestroyed(
       idb_transaction_id_));
 }
 
 int RendererWebIDBTransactionImpl::mode() const
 {
   int mode;
   RenderThread::current()->Send(new IndexedDBHostMsg_TransactionMode(
       idb_transaction_id_, &mode));
   return mode;
@@ skipping 26 matching lines @@
 }
 
 void RendererWebIDBTransactionImpl::setCallbacks(
     WebIDBTransactionCallbacks* callbacks)
 {
   IndexedDBDispatcher* dispatcher =
       RenderThread::current()->indexed_db_dispatcher();
   dispatcher->RegisterWebIDBTransactionCallbacks(callbacks,
                                                  idb_transaction_id_);
 }