Use devtools to set user agent in chromedriver

chrome/test/chromedriver/capabilities.cc

Index: chrome/test/chromedriver/capabilities.cc
diff --git a/chrome/test/chromedriver/capabilities.cc b/chrome/test/chromedriver/capabilities.cc
index 240318bf0702dcaeef7764405dee8df676876cb2..bc2502a913717fcf2f504e38f019a2abc1ea2698 100644
--- a/chrome/test/chromedriver/capabilities.cc
+++ b/chrome/test/chromedriver/capabilities.cc
@@ -114,7 +114,7 @@ Status ParseDeviceName(const std::string& device_name,
   capabilities->device_metrics.reset(device->device_metrics.release());
   // Don't override the user agent if blank (like for notebooks).
   if (!device->user_agent.empty())
-    capabilities->switches.SetSwitch("user-agent", device->user_agent);
+    capabilities->user_agent = device->user_agent;
 
   return Status(kOk);
 }
@@ -175,7 +175,7 @@ Status ParseMobileEmulation(const base::Value& option,
     if (!mobile_emulation->GetString("userAgent", &user_agent))
       return Status(kUnknownError, "'userAgent' must be a string");
 
-    capabilities->switches.SetSwitch("user-agent", user_agent);
+    capabilities->user_agent = user_agent;
   }
 
   return Status(kOk);