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

components/safe_browsing_db/v4_local_database_manager.cc

 // Copyright 2016 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.
 
 // This file should not be build on Android but is currently getting built.
 // TODO(vakh): Fix that: http://crbug.com/621647
 
 #include "components/safe_browsing_db/v4_local_database_manager.h"
 
 #include <vector>
@@ skipping 131 matching lines @@
   if (!v4_database_) {
     queued_checks_.push_back(std::move(check));
     return false;
   }
 
   FullHashToStoreAndHashPrefixesMap full_hash_to_store_and_hash_prefixes;
   if (!GetPrefixMatches(check, &full_hash_to_store_and_hash_prefixes)) {
     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;
 }
 
 bool V4LocalDatabaseManager::CheckDownloadUrl(
     const std::vector<GURL>& url_chain,
     Client* client) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   // TODO(vakh): Implement this skeleton.
   return true;
 }
@@ skipping 325 matching lines @@
 }
 
 void V4LocalDatabaseManager::UpdateRequestCompleted(
     std::unique_ptr<ParsedServerResponse> parsed_server_response) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   v4_database_->ApplyUpdate(std::move(parsed_server_response),
                             db_updated_callback_);
 }
 
 }  // namespace safe_browsing