Use devtools to set user agent in chromedriver

chrome/test/chromedriver/chrome_launcher.cc

Index: chrome/test/chromedriver/chrome_launcher.cc
diff --git a/chrome/test/chromedriver/chrome_launcher.cc b/chrome/test/chromedriver/chrome_launcher.cc
index 1592c2913c813c10936865934ba31f80edf66884..6d01ea6eab075c6efed0106d422fadea1e565cba 100644
--- a/chrome/test/chromedriver/chrome_launcher.cc
+++ b/chrome/test/chromedriver/chrome_launcher.cc
@@ -192,7 +192,8 @@ Status WaitForDevToolsAndCheckVersion(
 
   std::unique_ptr<DevToolsHttpClient> client(new DevToolsHttpClient(
       address, context_getter, socket_factory, std::move(device_metrics),
-      std::move(window_types), capabilities->page_load_strategy));
+      std::move(window_types), capabilities->page_load_strategy,
+      capabilities->user_agent));
   base::TimeTicks deadline =
       base::TimeTicks::Now() + base::TimeDelta::FromSeconds(60);
   Status status = client->Init(deadline - base::TimeTicks::Now());