Implement the target locator commands for ChromeDriver.

chrome/test/webdriver/commands/command.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/test/webdriver/commands/command.h"
 
 namespace webdriver {
 
 // Error message taken from:
 // http://code.google.com/p/selenium/wiki/JsonWireProtocol#Response_Status_Codes
@@ skipping 22 matching lines @@
 }
 
 bool Command::DoesPost() {
   return false;
 }
 
 bool Command::Init(Response* const response) {
   return true;
 }
 
+bool Command::IsNullParameter(const std::string& key) const {
+  Value* value;
+  return parameters_.get() &&
+         parameters_->Get(key, &value) &&
+         value->IsType(Value::TYPE_NULL);
+}
+
 bool Command::GetStringParameter(const std::string& key,
                                  string16* out) const {
   return parameters_.get() != NULL && parameters_->GetString(key, out);
 }
 
 bool Command::GetStringParameter(const std::string& key,
                                  std::string* out) const {
   return parameters_.get() != NULL && parameters_->GetString(key, out);
 }
 
@@ skipping 16 matching lines @@
                                      DictionaryValue** out) const {
   return parameters_.get() != NULL && parameters_->GetDictionary(key, out);
 }
 
 bool Command::GetListParameter(const std::string& key,
                                ListValue** out) const {
   return parameters_.get() != NULL && parameters_->GetList(key, out);
 }
 
 }  // namespace webdriver
-