ChromeDriver should be able to focus on a frame using its frame element,

chrome/test/webdriver/commands/target_locator_commands.h

 // 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.
 
 #ifndef CHROME_TEST_WEBDRIVER_COMMANDS_TARGET_LOCATOR_COMMANDS_H_
 #define CHROME_TEST_WEBDRIVER_COMMANDS_TARGET_LOCATOR_COMMANDS_H_
 
 #include <string>
 #include <vector>
 
 #include "chrome/test/webdriver/commands/webdriver_command.h"
 
 class DictionaryValue;
 
 namespace webdriver {
 
 class Response;
+class WebElementId;
 
 // Gets the current window handle.
 // REST URL: /session/:sessionId/window_handle
 class WindowHandleCommand : public WebDriverCommand {
  public:
   WindowHandleCommand(const std::vector<std::string>& path_segments,
                       DictionaryValue* parameters);
   virtual ~WindowHandleCommand();
 
   virtual bool DoesGet();
@@ skipping 41 matching lines @@
 class SwitchFrameCommand : public WebDriverCommand {
  public:
   SwitchFrameCommand(const std::vector<std::string>& path_segments,
                      DictionaryValue* parameters);
   virtual ~SwitchFrameCommand();
 
   virtual bool DoesPost();
   virtual void ExecutePost(Response* const response);
 
  private:
+  bool GetWebElementParameter(const std::string& key, WebElementId* out) const;
+
   DISALLOW_COPY_AND_ASSIGN(SwitchFrameCommand);
 };
 
 // Retrieves the active element on the current page.
 class ActiveElementCommand : public WebDriverCommand {
  public:
   ActiveElementCommand(const std::vector<std::string>& path_segments,
                        DictionaryValue* parameters);
   virtual ~ActiveElementCommand();
 
   virtual bool DoesPost();
   virtual void ExecutePost(Response* const response);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ActiveElementCommand);
 };
 
 }  // namespace webdriver
 
 #endif  // CHROME_TEST_WEBDRIVER_COMMANDS_TARGET_LOCATOR_COMMANDS_H_