Implement the target locator commands for ChromeDriver.

chrome/test/webdriver/commands/command.cc

Index: chrome/test/webdriver/commands/command.cc
diff --git a/chrome/test/webdriver/commands/command.cc b/chrome/test/webdriver/commands/command.cc
index 29ea60f8a570d0aceffab14e71b2dd79efe94f1d..cb9e67059d63fff4af2a54fa5b99354f024602ae 100644
--- a/chrome/test/webdriver/commands/command.cc
+++ b/chrome/test/webdriver/commands/command.cc
@@ -40,6 +40,13 @@ 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);
@@ -76,4 +83,3 @@ bool Command::GetListParameter(const std::string& key,
 }
 
 }  // namespace webdriver
-