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

chrome/test/webdriver/session.h

Index: chrome/test/webdriver/session.h
diff --git a/chrome/test/webdriver/session.h b/chrome/test/webdriver/session.h
index 3f075e014d630c90e929db680bbd7b07c072a15e..8292f8039f3d2bf49c6f9b911a3110d4255ce2f4 100644
--- a/chrome/test/webdriver/session.h
+++ b/chrome/test/webdriver/session.h
@@ -79,9 +79,7 @@ class Session {
   // It |user_data_dir| is empty, it will use a temporary dir.
   // Returns true on success. On failure, the session will delete
   // itself and return an error code.
-  Error* Init(const FilePath& browser_exe,
-              const FilePath& user_data_dir,
-              const CommandLine& options);
+  Error* Init(const Automation::BrowserOptions& options);
 
   // Should be called before executing a command. Performs necessary waits
   // and frame switching.
@@ -323,9 +321,7 @@ class Session {
   void RunSessionTaskOnSessionThread(
       Task* task,
       base::WaitableEvent* done_event);
-  void InitOnSessionThread(const FilePath& browser_exe,
-                           const FilePath& user_data_dir,
-                           const CommandLine& options,
+  void InitOnSessionThread(const Automation::BrowserOptions& options,
                            Error** error);
   void TerminateOnSessionThread();