Fix for potential crash due to scheduling an empty callback.

components/component_updater/component_updater_service.cc

 // Copyright 2014 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 "components/component_updater/component_updater_service.h"
 
 #include <algorithm>
 #include <map>
 #include <string>
 #include <utility>
@@ skipping 234 matching lines @@
   }
 
   callback.Run();  // Unblock the request if the request can't be throttled.
 }
 
 void CrxUpdateService::OnDemandUpdate(const std::string& id,
                                       const Callback& callback) {
   DCHECK(thread_checker_.CalledOnValidThread());
 
   if (!GetComponent(id)) {
-    base::ThreadTaskRunnerHandle::Get()->PostTask(
-        FROM_HERE,
-        base::Bind(callback, update_client::Error::INVALID_ARGUMENT));
+    if (!callback.is_null()) {
+      base::ThreadTaskRunnerHandle::Get()->PostTask(
+          FROM_HERE,
+          base::Bind(callback, update_client::Error::INVALID_ARGUMENT));
+    }
     return;
   }
 
   OnDemandUpdateInternal(id, callback);
 }
 
 bool CrxUpdateService::OnDemandUpdateWithCooldown(const std::string& id) {
   DCHECK(thread_checker_.CalledOnValidThread());
 
   DCHECK(GetComponent(id));
@@ skipping 189 matching lines @@
 // is the job of the browser process.
 // TODO(sorin): consider making this a singleton.
 std::unique_ptr<ComponentUpdateService> ComponentUpdateServiceFactory(
     const scoped_refptr<Configurator>& config) {
   DCHECK(config);
   auto update_client = update_client::UpdateClientFactory(config);
   return base::MakeUnique<CrxUpdateService>(config, std::move(update_client));
 }
 
 }  // namespace component_updater