Refactor chromedriver's script execution to reduce amount of custom Value parsing.

chrome/test/webdriver/utility_functions_unittest.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 <set>
-#include <string>
-
-#include "chrome/test/webdriver/utility_functions.h"
-#include "testing/gtest/include/gtest/gtest.h"
-
-TEST(RandomIDTest, CanGenerateSufficientlyRandomIDs) {
-  std::set<std::string> generated_ids;
-  for (int i = 0; i < 10000; ++i) {
-    std::string id = webdriver::GenerateRandomID();
-    ASSERT_EQ(32u, id.length());
-    ASSERT_TRUE(generated_ids.end() == generated_ids.find(id))
-        << "Generated duplicate ID: " << id
-        << " on iteration " << i;
-    generated_ids.insert(id);
-  }
-}