Use devtools to set user agent in chromedriver

chrome/test/chromedriver/chrome/mobile_emulation_override_manager_unittest.cc

Index: chrome/test/chromedriver/chrome/mobile_emulation_override_manager_unittest.cc
diff --git a/chrome/test/chromedriver/chrome/mobile_emulation_override_manager_unittest.cc b/chrome/test/chromedriver/chrome/mobile_emulation_override_manager_unittest.cc
index e9802051c45cbff1eca6cad068b56b1fec8212c3..256c276cafc75ed1ad0cfc7c5f8ef07a8326e503 100644
--- a/chrome/test/chromedriver/chrome/mobile_emulation_override_manager_unittest.cc
+++ b/chrome/test/chromedriver/chrome/mobile_emulation_override_manager_unittest.cc
@@ -39,7 +39,8 @@ void AssertDeviceMetricsCommand(const Command& command,
 TEST(MobileEmulationOverrideManager, SendsCommandWithTouchOnConnect) {
   RecorderDevToolsClient client;
   DeviceMetrics device_metrics(1, 2, 3.0, true, true);
-  MobileEmulationOverrideManager manager(&client, &device_metrics);
+  MobileEmulationOverrideManager manager(&client, &device_metrics,
+                                         std::string());
   ASSERT_EQ(0u, client.commands_.size());
   ASSERT_EQ(kOk, manager.OnConnected(&client).code());
 
@@ -53,7 +54,8 @@ TEST(MobileEmulationOverrideManager, SendsCommandWithTouchOnConnect) {
 TEST(MobileEmulationOverrideManager, SendsCommandWithoutTouchOnConnect) {
   RecorderDevToolsClient client;
   DeviceMetrics device_metrics(1, 2, 3.0, false, true);
-  MobileEmulationOverrideManager manager(&client, &device_metrics);
+  MobileEmulationOverrideManager manager(&client, &device_metrics,
+                                         std::string());
   ASSERT_EQ(0u, client.commands_.size());
   ASSERT_EQ(kOk, manager.OnConnected(&client).code());
 
@@ -67,7 +69,8 @@ TEST(MobileEmulationOverrideManager, SendsCommandWithoutTouchOnConnect) {
 TEST(MobileEmulationOverrideManager, SendsCommandOnNavigation) {
   RecorderDevToolsClient client;
   DeviceMetrics device_metrics(1, 2, 3.0, true, true);
-  MobileEmulationOverrideManager manager(&client, &device_metrics);
+  MobileEmulationOverrideManager manager(&client, &device_metrics,
+                                         std::string());
   base::DictionaryValue main_frame_params;
   ASSERT_EQ(kOk,
             manager.OnEvent(&client, "Page.frameNavigated", main_frame_params)