Move SafeBrowsing to the blocking pool via an experiment.

chrome/browser/safe_browsing/database_manager.h

Index: chrome/browser/safe_browsing/database_manager.h
diff --git a/chrome/browser/safe_browsing/database_manager.h b/chrome/browser/safe_browsing/database_manager.h
index d23962098db0394da3ae06cf5dd4147d9da94569..389150d49c4582e2e1945d6b02a3e5ccb50ef167 100644
--- a/chrome/browser/safe_browsing/database_manager.h
+++ b/chrome/browser/safe_browsing/database_manager.h
@@ -399,6 +399,10 @@ class SafeBrowsingDatabaseManager
   // 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.
+  scoped_refptr<base::SequencedTaskRunner> safe_browsing_task_runner_;
+
   // Indicates if we're currently in an update cycle.
   bool update_in_progress_;