Suppress IO-on-wrong-thread DCHECK during file downloads....

chrome/browser/icon_manager_linux.cc

 // Copyright (c) 2009 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/icon_manager.h"
 
 #include "base/mime_util.h"
+#include "base/threading/thread_restrictions.h"
 
 IconGroupID IconManager::GetGroupIDFromFilepath(const FilePath& filepath) {
+  // It turns out the call to mime_util::GetFileMimeType below does IO, but
+  // callers of GetGroupIDFromFilepath assume it does not do IO (the Windows
+  // and Mac implementations do not). We should fix this by either not doing IO
+  // in this method, or reworking callers to avoid calling it on the UI thread.
+  // See crbug.com/72740.
+  base::ThreadRestrictions::ScopedAllowIO allow_io;
+
   return mime_util::GetFileMimeType(filepath);
 }