Remove user agent from HeadlessBrowserContextOptions.

headless/lib/browser/headless_browser_context_options.cc

Index: headless/lib/browser/headless_browser_context_options.cc
diff --git a/headless/lib/browser/headless_browser_context_options.cc b/headless/lib/browser/headless_browser_context_options.cc
index f9fa8248e5b57f9fc7f05ccd470f3b29f6409fe9..e31158bdc4c70e88e66666ba15d86d1df9d0ca83 100644
--- a/headless/lib/browser/headless_browser_context_options.cc
+++ b/headless/lib/browser/headless_browser_context_options.cc
@@ -42,7 +42,7 @@ const std::string& HeadlessBrowserContextOptions::product_name_and_version()
 }
 
 const std::string& HeadlessBrowserContextOptions::user_agent() const {
-  return ReturnOverriddenValue(user_agent_, browser_options_->user_agent);
+  return browser_options_->user_agent;
 }
 
 const net::HostPortPair& HeadlessBrowserContextOptions::proxy_server() const {