Implement a poor man's PostAfterStartupTask() function.

content/public/browser/content_browser_client.cc

Index: content/public/browser/content_browser_client.cc
diff --git a/content/public/browser/content_browser_client.cc b/content/public/browser/content_browser_client.cc
index 1ce7105dfda6ddff3aae9f7487691fa25330c0c7..9980773685ec843b162a47b8d9bc964b29d2c037 100644
--- a/content/public/browser/content_browser_client.cc
+++ b/content/public/browser/content_browser_client.cc
@@ -16,6 +16,13 @@ BrowserMainParts* ContentBrowserClient::CreateBrowserMainParts(
   return nullptr;
 }
 
+void ContentBrowserClient::PostAfterStartupTask(
+    const tracked_objects::Location& from_here,
+    const scoped_refptr<base::TaskRunner>& task_runner,
+    const base::Closure& task) {
+  task_runner->PostTask(from_here, task);
+}
+
 WebContentsViewDelegate* ContentBrowserClient::GetWebContentsViewDelegate(
     WebContents* web_contents) {
   return nullptr;