Implement the target locator commands for ChromeDriver.

chrome/test/webdriver/commands/command.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_COMMAND_H_
 #define CHROME_TEST_WEBDRIVER_COMMANDS_COMMAND_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 36 matching lines @@
 
  protected:
 
   // Returns the path variable encoded at the |i|th index (0-based) in the
   // request URL for this command. If the index is out of bounds, an empty
   // string will be returned.
   inline std::string GetPathVariable(const size_t i) const {
     return i < path_segments_.size() ? path_segments_.at(i) : "";
   }
 
-  // Provides the command parameter with the given |key| as a UTF-16 string.
+  // Returns true if the command parameter with the given |key| exists and is
+  // a null value.
+  bool IsNullParameter(const std::string& key) const;
+
+  // Returns the command parameter with the given |key| as a UTF-16 string.
   // Returns true on success.
   bool GetStringParameter(const std::string& key, string16* out) const;
 
   // Provides the command parameter with the given |key| as a UTF-8 string.
   // Returns true on success.
   bool GetStringParameter(const std::string& key, std::string* out) const;
 
   // Provides the command parameter with the given |key| as a ASCII string.
   // Returns true on success.
   bool GetStringASCIIParameter(const std::string& key, std::string* out) const;
@@ skipping 25 matching lines @@
   // is printed for every object deallocted.  Since every incomming command to
   // chrome driver is allocated a new thread, the release pool is declared here.
   base::mac::ScopedNSAutoreleasePool autorelease_pool;
 
   DISALLOW_COPY_AND_ASSIGN(Command);
 };
 
 }  // namespace webdriver
 
 #endif  // CHROME_TEST_WEBDRIVER_COMMANDS_COMMAND_H_
-