Fix for potential crash due to scheduling an empty callback.

components/component_updater/component_updater_service.cc

Index: components/component_updater/component_updater_service.cc
diff --git a/components/component_updater/component_updater_service.cc b/components/component_updater/component_updater_service.cc
index d6c4261b186970fda6edc11df75d3fb580e8fd1e..dddde69d319114f78b4d6269b853a7ac8c35877c 100644
--- a/components/component_updater/component_updater_service.cc
+++ b/components/component_updater/component_updater_service.cc
@@ -252,9 +252,11 @@ void CrxUpdateService::OnDemandUpdate(const std::string& id,
   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;
   }