Make installation of the elevation service optional.

There are cases where the elevation service may fail to install, for
instance, if security software prevents installation.

Bug: 1023080
Change-Id: Ibab20f2ee44395254ef702a460f8fad60836e682
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2168825Reviewed-by: Greg Thompson <grt@chromium.org>
Commit-Queue: S. Ganesh <ganesh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#763421}

chrome/installer/setup/install_worker.cc

@@ -411,9 +411,10 @@ void AddElevationServiceWorkItems(const base::FilePath& elevation_service_path,
   }
 
   list->AddWorkItem(new InstallServiceWorkItem(
-      install_static::GetElevationServiceName(),
-      install_static::GetElevationServiceDisplayName(),
-      base::CommandLine(elevation_service_path)));
+                        install_static::GetElevationServiceName(),
+                        install_static::GetElevationServiceDisplayName(),
+                        base::CommandLine(elevation_service_path)))
+      ->set_best_effort(true);
 
   list->AddCreateRegKeyWorkItem(root, clsid_reg_path, WorkItem::kWow64Default);
   list->AddSetRegValueWorkItem(root, clsid_reg_path, WorkItem::kWow64Default,