Use devtools to set user agent in chromedriver

chrome/test/chromedriver/chrome/mobile_emulation_override_manager.cc

Index: chrome/test/chromedriver/chrome/mobile_emulation_override_manager.cc
diff --git a/chrome/test/chromedriver/chrome/mobile_emulation_override_manager.cc b/chrome/test/chromedriver/chrome/mobile_emulation_override_manager.cc
index 95e56ff1e95d8c55ecf293e9fd1f33f5f7b46ece..8aa8385c3a91c50596c6dbe27f04bb9d766b2c2d 100644
--- a/chrome/test/chromedriver/chrome/mobile_emulation_override_manager.cc
+++ b/chrome/test/chromedriver/chrome/mobile_emulation_override_manager.cc
@@ -11,10 +11,12 @@
 
 MobileEmulationOverrideManager::MobileEmulationOverrideManager(
     DevToolsClient* client,
-    const DeviceMetrics* device_metrics)
+    const DeviceMetrics* device_metrics,
+    std::string user_agent)
     : client_(client),
-      overridden_device_metrics_(device_metrics) {
-  if (overridden_device_metrics_)
+      overridden_device_metrics_(device_metrics),
+      overridden_user_agent_(user_agent) {
+  if (overridden_device_metrics_ || !overridden_user_agent_.empty())
     client_->AddListener(this);
 }
 
@@ -42,6 +44,19 @@ bool MobileEmulationOverrideManager::IsEmulatingTouch() {
 }
 
 Status MobileEmulationOverrideManager::ApplyOverrideIfNeeded() {
+  if (!overridden_user_agent_.empty()) {
+    base::DictionaryValue net_enable_params, user_agent_params;
+    net_enable_params.SetInteger("maxTotalBufferSize", 0);
+    net_enable_params.SetInteger("maxResourceBufferSize", 0);
+    Status status = client_->SendCommand("Network.enable", net_enable_params);
+
+    user_agent_params.SetString("userAgent", overridden_user_agent_);
+    status =
+        client_->SendCommand("Network.setUserAgentOverride", user_agent_params);
+    if (status.IsError())
+      return status;
+  }
+
   if (overridden_device_metrics_ == NULL)
     return Status(kOk);