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

chrome/browser/automation/automation_provider.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/automation/automation_provider.h"
 
 #include <set>
 
 #include "base/callback.h"
 #include "base/debug/trace_event.h"
@@ skipping 138 matching lines @@
     if (effective_channel_id.length() <= 0)
       return false;
 
     reinitialize_on_channel_error_ = true;
   }
 
   if (!automation_resource_message_filter_.get()) {
     automation_resource_message_filter_ = new AutomationResourceMessageFilter;
   }
 
+  base::ThreadRestrictions::ScopedAllowIO allow_io;
   channel_.reset(new IPC::ChannelProxy(
       effective_channel_id,
       GetChannelMode(use_named_interface),
       this,
       BrowserThread::GetMessageLoopProxyForThread(BrowserThread::IO)));
   channel_->AddFilter(automation_resource_message_filter_);
 
 #if defined(OS_CHROMEOS)
   // Wait for the network manager to initialize.
   // The observer will delete itself when done.
@@ skipping 791 matching lines @@
     }
   }
 }
 
 void AutomationProvider::SaveAsAsync(int tab_handle) {
   NavigationController* tab = NULL;
   TabContents* tab_contents = GetTabContentsForHandle(tab_handle, &tab);
   if (tab_contents)
     tab_contents->OnSavePage();
 }