Move SafeBrowsing to the blocking pool via an experiment.

chrome/browser/safe_browsing/database_manager.h

 // 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.
 //
 // The Safe Browsing service is responsible for downloading anti-phishing and
 // anti-malware tables and checking urls against them.
 
 #ifndef CHROME_BROWSER_SAFE_BROWSING_DATABASE_MANAGER_H_
 #define CHROME_BROWSER_SAFE_BROWSING_DATABASE_MANAGER_H_
 
@@ skipping 381 matching lines @@
   // Indicate if the unwanted software blacklist should be enabled.
   bool enable_unwanted_software_blacklist_;
 
   // The SafeBrowsing thread that runs database operations.
   //
   // Note: Functions that run on this thread should run synchronously and return
   // to the IO thread, not post additional tasks back to this thread, lest we
   // cause a race condition at shutdown time that leads to a database leak.
   scoped_ptr<base::Thread> safe_browsing_thread_;
 
+  // The sequenced task runner for this object, used to verify that its state
+  // is only ever accessed in sequence via the runner.

[gab, 2015/02/19 14:38:23]

It's mainly used to post tasks to the safe_browsing_thread_ of BlockingPool
variants thereof -- verification is only secondary isn't it?

[Alexei Svitkine (slow), 2015/02/20 15:42:44]

Indeed. Updated comment.

+  scoped_refptr<base::SequencedTaskRunner> safe_browsing_task_runner_;
+
   // Indicates if we're currently in an update cycle.
   bool update_in_progress_;
 
   // When true, newly fetched chunks may not in the database yet since the
   // database is still updating.
   bool database_update_in_progress_;
 
   // Indicates if we're in the midst of trying to close the database.  If this
   // is true, nothing on the IO thread should access the database.
   bool closing_database_;
 
   std::deque<QueuedCheck> queued_checks_;
 
   // Timeout to use for safe browsing checks.
   base::TimeDelta check_timeout_;
 
   DISALLOW_COPY_AND_ASSIGN(SafeBrowsingDatabaseManager);
 };
 
 #endif  // CHROME_BROWSER_SAFE_BROWSING_DATABASE_MANAGER_H_