Use devtools to set user agent in chromedriver

chrome/test/chromedriver/chrome/devtools_http_client.h

Index: chrome/test/chromedriver/chrome/devtools_http_client.h
diff --git a/chrome/test/chromedriver/chrome/devtools_http_client.h b/chrome/test/chromedriver/chrome/devtools_http_client.h
index b2182fff14c0b9e7b7b16bdc953219ec3bd76576..6edf0c78613cabca2471ba1a6e9ca1b288f8ebff 100644
--- a/chrome/test/chromedriver/chrome/devtools_http_client.h
+++ b/chrome/test/chromedriver/chrome/devtools_http_client.h
@@ -79,7 +79,8 @@ class DevToolsHttpClient {
                      const SyncWebSocketFactory& socket_factory,
                      std::unique_ptr<DeviceMetrics> device_metrics,
                      std::unique_ptr<std::set<WebViewInfo::Type>> window_types,
-                     std::string page_load_strategy);
+                     std::string page_load_strategy,
+                     std::string user_agent);
   ~DevToolsHttpClient();
 
   Status Init(const base::TimeDelta& timeout);
@@ -95,6 +96,7 @@ class DevToolsHttpClient {
   const BrowserInfo* browser_info();
   const DeviceMetrics* device_metrics();
   bool IsBrowserWindow(const WebViewInfo& view) const;
+  const std::string& user_agent() const;
 
  private:
   Status CloseFrontends(const std::string& for_client_id);
@@ -110,6 +112,7 @@ class DevToolsHttpClient {
   std::unique_ptr<DeviceMetrics> device_metrics_;
   std::unique_ptr<std::set<WebViewInfo::Type>> window_types_;
   std::string page_load_strategy_;
+  std::string user_agent_;
 
   DISALLOW_COPY_AND_ASSIGN(DevToolsHttpClient);
 };