Fix BrowsingDataCounter race condition

chrome/browser/browsing_data/media_licenses_counter.cc

 // Copyright 2016 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/browsing_data/media_licenses_counter.h"
 
 #include <stdint.h>
 
 #include "base/memory/ptr_util.h"
 #include "base/memory/ref_counted.h"
@@ skipping 45 matching lines @@
       weak_ptr_factory_(this) {}
 
 MediaLicensesCounter::~MediaLicensesCounter() {}
 
 const char* MediaLicensesCounter::GetPrefName() const {
   return browsing_data::prefs::kDeleteMediaLicenses;
 }
 
 void MediaLicensesCounter::Count() {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  // Cancel existing requests.
+  weak_ptr_factory_.InvalidateWeakPtrs();
   scoped_refptr<storage::FileSystemContext> filesystem_context =
       make_scoped_refptr(
           content::BrowserContext::GetDefaultStoragePartition(profile_)
               ->GetFileSystemContext());
   base::PostTaskAndReplyWithResult(
       filesystem_context->default_file_task_runner(), FROM_HERE,
       base::Bind(&CountOriginsOnFileTaskRunner,
                  base::RetainedRef(filesystem_context)),
       base::Bind(&MediaLicensesCounter::OnContentLicensesObtained,
                  weak_ptr_factory_.GetWeakPtr()));
 }
 
 void MediaLicensesCounter::OnContentLicensesObtained(
     const std::set<GURL>& origins) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   ReportResult(base::MakeUnique<MediaLicenseResult>(this, origins));
 }