Disallow UI/IO thread blocking on any other thread.

net/disk_cache/backend_impl.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.
 
 #include "net/disk_cache/backend_impl.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/file_path.h"
 #include "base/file_util.h"
@@ skipping 351 matching lines @@
     // possible at this time, at the price of leaving dirty entries behind.
     background_queue_.DropPendingIO();
   }
 
   if (background_queue_.BackgroundIsCurrentThread()) {
     // Unit tests may use the same thread for everything.
     CleanupCache();
   } else {
     background_queue_.background_thread()->PostTask(
         FROM_HERE, base::Bind(&FinalCleanupCallback, base::Unretained(this)));
+    // http://crbug.com/74623
+    base::ThreadRestrictions::ScopedAllowWait allow_wait;
     done_.Wait();
   }
 }
 
 // If the initialization of the cache fails, and force is true, we will discard
 // the whole cache and create a new one. In order to process a potentially large
 // number of files, we'll rename the cache folder to old_ + original_name +
 // number, (located on the same parent folder), and spawn a worker thread to
 // delete all the files on all the stale cache folders. The whole process can
 // still fail if we are not able to rename the cache folder (for instance due to
@@ skipping 1788 matching lines @@
     if (total_memory > kMaxBuffersSize || total_memory <= 0)
       total_memory = kMaxBuffersSize;
 
     done = true;
   }
 
   return static_cast<int>(total_memory);
 }
 
 }  // namespace disk_cache