Tiny: Post PerformFullHashCheck on IO thread, instead of calling it synchronously.

components/safe_browsing_db/v4_local_database_manager.cc

Index: components/safe_browsing_db/v4_local_database_manager.cc
diff --git a/components/safe_browsing_db/v4_local_database_manager.cc b/components/safe_browsing_db/v4_local_database_manager.cc
index 65916ba8ea63a77a7d0be73760239c84bef4e02a..e640abe9d62121bd5014e2fd59ca4ca61eaa795d 100644
--- a/components/safe_browsing_db/v4_local_database_manager.cc
+++ b/components/safe_browsing_db/v4_local_database_manager.cc
@@ -149,7 +149,13 @@ bool V4LocalDatabaseManager::CheckBrowseUrl(const GURL& url, Client* client) {
     return true;
   }
 
-  PerformFullHashCheck(std::move(check), full_hash_to_store_and_hash_prefixes);
+  // Post the task to check full hashes back on the IO thread to follow the
+  // documented behavior of CheckBrowseUrl.
+  BrowserThread::PostTask(
+      BrowserThread::IO, FROM_HERE,
+      base::Bind(&V4LocalDatabaseManager::PerformFullHashCheck, this,
+                 base::Passed(std::move(check)),
+                 full_hash_to_store_and_hash_prefixes));
   return false;
 }