Expose UkmService to content/

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 f285b85546fc246b3d42b735f82673e833d335f3..71e2b9d4ddf30cebe47fd097a27e98b207ac3f8c 100644
--- a/content/public/browser/content_browser_client.cc
+++ b/content/public/browser/content_browser_client.cc
@@ -462,6 +462,10 @@ ContentBrowserClient::GetMemoryCoordinatorDelegate() {
   return nullptr;
 }
 
+::ukm::UkmService* ContentBrowserClient::GetUkmService() {
+  return nullptr;
+}
+
 std::unique_ptr<base::TaskScheduler::InitParams>
 ContentBrowserClient::GetTaskSchedulerInitParams() {
   return nullptr;