Use devtools to set user agent in chromedriver

chrome/test/chromedriver/chrome/web_view_impl.h

Index: chrome/test/chromedriver/chrome/web_view_impl.h
diff --git a/chrome/test/chromedriver/chrome/web_view_impl.h b/chrome/test/chromedriver/chrome/web_view_impl.h
index cd0fed3de1ae59d60af5911adcbf2966dff5bf3c..2f0435dd4083867c18c6f891480890ec00e90446 100644
--- a/chrome/test/chromedriver/chrome/web_view_impl.h
+++ b/chrome/test/chromedriver/chrome/web_view_impl.h
@@ -41,7 +41,8 @@ class WebViewImpl : public WebView {
               const BrowserInfo* browser_info,
               std::unique_ptr<DevToolsClient> client,
               const DeviceMetrics* device_metrics,
-              std::string page_load_strategy);
+              std::string page_load_strategy,
+              std::string user_agent);
   ~WebViewImpl() override;
 
   // Overridden from WebView: