Disallow UI/IO thread blocking on any other thread.

net/base/file_stream_posix.cc

 // Copyright (c) 2012 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.
 
 // For 64-bit file access (off_t = off64_t, lseek64, etc).
 #define _FILE_OFFSET_BITS 64
 
 #include "net/base/file_stream.h"
 
 #include <sys/types.h>
@@ skipping 626 matching lines @@
 
 void FileStreamPosix::OnClosed(const CompletionCallback& callback) {
   file_ = base::kInvalidPlatformFileValue;
 
   // Reset this before Run() as Run() may issue a new async operation.
   ResetOnIOComplete();
   callback.Run(OK);
 }
 
 void FileStreamPosix::WaitForIOCompletion() {
+  base::ThreadRestrictions::ScopedAllowWait allow_wait;
   if (on_io_complete_.get()) {
     on_io_complete_->Wait();
     on_io_complete_.reset();
   }
 }
 
 }  // namespace net