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

chrome/test/webdriver/commands/target_locator_commands.h

Index: chrome/test/webdriver/commands/target_locator_commands.h
===================================================================
--- chrome/test/webdriver/commands/target_locator_commands.h	(revision 79141)
+++ chrome/test/webdriver/commands/target_locator_commands.h	(working copy)
@@ -15,6 +15,7 @@
 namespace webdriver {
 
 class Response;
+class WebElementId;
 
 // Gets the current window handle.
 // REST URL: /session/:sessionId/window_handle
@@ -76,6 +77,8 @@
   virtual void ExecutePost(Response* const response);
 
  private:
+  bool GetWebElementParameter(const std::string& key, WebElementId* out) const;
+
   DISALLOW_COPY_AND_ASSIGN(SwitchFrameCommand);
 };