Correct const accessors in base/values.(h|cc)

chrome/test/webdriver/commands/screenshot_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/screenshot_command.h"
 
 #include <string>
 #include <vector>
 
 #include "base/base64.h"
 #include "base/values.h"
 #include "chrome/test/webdriver/commands/response.h"
 #include "chrome/test/webdriver/webdriver_error.h"
 #include "chrome/test/webdriver/webdriver_session.h"
 
 namespace webdriver {
 
 ScreenshotCommand::ScreenshotCommand(const std::vector<std::string>& ps,
-                                     const DictionaryValue* const parameters)
+                                     DictionaryValue* const parameters)
     : WebDriverCommand(ps, parameters) {}
 
 ScreenshotCommand::~ScreenshotCommand() {}
 
 bool ScreenshotCommand::DoesGet() {
   return true;
 }
 
 void ScreenshotCommand::ExecuteGet(Response* const response) {
   std::string raw_bytes;
   Error* error = session_->GetScreenShot(&raw_bytes);
   if (error) {
     response->SetError(error);
     return;
   }
 
   // Convert the raw binary data to base 64 encoding for webdriver.
   std::string base64_screenshot;
   if (!base::Base64Encode(raw_bytes, &base64_screenshot)) {
     response->SetError(new Error(
         kUnknownError, "Encoding the PNG to base64 format failed"));
     return;
   }
 
   response->SetValue(new StringValue(base64_screenshot));
 }
 
 }  // namespace webdriver