Let pyauto create an attached webdriver instance to manipulate web pages.

chrome/browser/automation/testing_automation_provider.h

Index: chrome/browser/automation/testing_automation_provider.h
diff --git a/chrome/browser/automation/testing_automation_provider.h b/chrome/browser/automation/testing_automation_provider.h
index 5052447d16ee153f1e2255ceac3cb663b758ba75..fbd486c61acd0c1d6e4befb22c6f3a6258992e58 100644
--- a/chrome/browser/automation/testing_automation_provider.h
+++ b/chrome/browser/automation/testing_automation_provider.h
@@ -1150,6 +1150,14 @@ class TestingAutomationProvider : public AutomationProvider,
   void UpdateExtensionsNow(base::DictionaryValue* args,
                            IPC::Message* reply_message);
 
+  // Creates a new |TestingAutomationProvider| that opens a server channel
+  // for the given |channel_id|.
+  // The server channel will be available for connection when this returns.
+  // Example:
+  //   input: { "channel_id": "testChannel123" }
+  void CreateNewAutomationProvider(base::DictionaryValue* args,
+                                   IPC::Message* reply_message);
+
 #if defined(OS_CHROMEOS)
   // Login.
   void GetLoginInfo(base::DictionaryValue* args, IPC::Message* reply_message);