[chromedriver] Implement SwitchToFrame command.

chrome/test/chromedriver/chrome.h

 // Copyright (c) 2012 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_CHROMEDRIVER_CHROME_H_
 #define CHROME_TEST_CHROMEDRIVER_CHROME_H_
 
 #include <string>
 
 #include "base/memory/scoped_ptr.h"
 
 namespace base {
 class ListValue;
 class Value;
 }
 
 class Status;
 
 class Chrome {
  public:
   virtual ~Chrome() {}
 
+  // Load a given URL in the main frame.
   virtual Status Load(const std::string& url) = 0;
-  virtual Status EvaluateScript(const std::string& expression,
+
+  // Evaluates a JavaScript expression in a specified frame and returns
+  // the result. |frame| is a frame ID or an empty string for the main frame.
+  // If the expression evaluates to a element, it will be bound to a unique ID
+  // (per frame) and the ID will be returned.
+  virtual Status EvaluateScript(const std::string& frame,
+                                const std::string& expression,
                                 scoped_ptr<base::Value>* result) = 0;
-  virtual Status CallFunction(const std::string& function,
+
+  // Calls a JavaScript function in a specified frame with the given args and
+  // returns the result. |frame| is a frame ID or an empty string for the main
+  // frame. |args| may contain IDs that refer to previously returned elements.
+  // These will be translated back to their referred objects before invoking the
+  // function.
+  virtual Status CallFunction(const std::string& frame,
+                              const std::string& function,
                               const base::ListValue& args,
                               scoped_ptr<base::Value>* result) = 0;
+
+  // Gets the frame ID for a frame element returned by invoking the given
+  // JavaScript function. |frame| is a frame ID or an empty string for the main
+  // frame.
+  virtual Status GetFrameByFunction(const std::string& frame,
+                                    const std::string& function,
+                                    const base::ListValue& args,
+                                    std::string* out_frame) = 0;
+
+  // Quits Chrome.
   virtual Status Quit() = 0;
 };
 
 #endif  // CHROME_TEST_CHROMEDRIVER_CHROME_H_