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 a71c8175dbc2a1f673c277704657fd8d3ac34f15..34ea1d5a50428ac1dd68ad6a5b863af4a35a468b 100644
--- a/chrome/test/webdriver/session.h
+++ b/chrome/test/webdriver/session.h
@@ -65,9 +65,7 @@ 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::InitOptions& options);
 
   // Terminates this session and deletes itself.
   void Terminate();
@@ -294,9 +292,7 @@ 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::InitOptions& options,
                            Error** error);
   void TerminateOnSessionThread();