Remove all code related to the PreRead field trial.

components/startup_metric_utils/common/pre_read_field_trial_utils_win.cc

-// Copyright 2015 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 "components/startup_metric_utils/common/pre_read_field_trial_utils_win.h"
-
-#include "base/callback.h"
-#include "base/logging.h"
-#include "base/metrics/field_trial.h"
-#include "base/strings/string_util.h"
-#include "base/strings/utf_string_conversions.h"
-#include "base/win/registry.h"
-#include "components/variations/variations_associated_data.h"
-
-namespace startup_metric_utils {
-
-namespace {
-
-// Name of the pre-read field trial. This name is used to get the pre-read group
-// to use for the next startup from base::FieldTrialList.
-const char kPreReadFieldTrialName[] = "PreRead";
-
-// Name of the synthetic pre-read field trial. A synthetic field trial is
-// registered so that UMA metrics recorded during the current startup are
-// annotated with the pre-read group that is actually used during this startup.
-const char kPreReadSyntheticFieldTrialName[] = "SyntheticPreRead";
-
-// Variation names for the PreRead field trial. All variations change the
-// default behavior, i.e. the default is the inverse of the variation. Thus,
-// variations that cancel something that is done by default have a negative
-// name.
-const base::char16 kNoPreReadVariationName[] = L"NoPreRead";
-const base::char16 kHighPriorityVariationName[] = L"HighPriority";
-const base::char16 kPrefetchVirtualMemoryVariationName[] =
-    L"PrefetchVirtualMemory";
-
-// Registry key in which the PreRead field trial group is stored.
-const base::char16 kPreReadFieldTrialRegistryKey[] = L"\\PreReadFieldTrial";
-
-// Pre-read options to use for the current process. This is initialized by
-// InitializePreReadOptions().
-PreReadOptions g_pre_read_options = {};
-
-// Returns the registry path in which the PreRead group is stored.
-base::string16 GetPreReadRegistryPath(
-    const base::string16& product_registry_path) {
-  return product_registry_path + kPreReadFieldTrialRegistryKey;
-}
-
-// Returns true if |key| has a value named |name| which is not zero.
-bool ReadBool(const base::win::RegKey& key, const base::char16* name) {
-  DWORD value = 0;
-  return key.ReadValueDW(name, &value) == ERROR_SUCCESS && value != 0;
-}
-
-}  // namespace
-
-void InitializePreReadOptions(const base::string16& product_registry_path) {
-  DCHECK(!product_registry_path.empty());
-
-#if DCHECK_IS_ON()
-  static bool initialized = false;
-  DCHECK(!initialized);
-  initialized = true;
-#endif  // DCHECK_IS_ON()
-
-  // Open the PreRead field trial's registry key.
-  const base::string16 registry_path =
-      GetPreReadRegistryPath(product_registry_path);
-  const base::win::RegKey key(HKEY_CURRENT_USER, registry_path.c_str(),
-                              KEY_QUERY_VALUE);
-
-  // Set the PreRead field trial's options.
-  g_pre_read_options.pre_read = !ReadBool(key, kNoPreReadVariationName);
-  g_pre_read_options.high_priority = ReadBool(key, kHighPriorityVariationName);
-  g_pre_read_options.prefetch_virtual_memory =
-      ReadBool(key, kPrefetchVirtualMemoryVariationName);
-}
-
-PreReadOptions GetPreReadOptions() {
-  return g_pre_read_options;
-}
-
-void UpdatePreReadOptions(const base::string16& product_registry_path) {
-  DCHECK(!product_registry_path.empty());
-
-  const base::string16 registry_path =
-      GetPreReadRegistryPath(product_registry_path);
-
-  // Clear the experiment key. That way, when the trial is shut down, the
-  // registry will be cleaned automatically. Also, this prevents variation
-  // params from the previous group to stay in the registry when the group is
-  // updated.
-  base::win::RegKey(HKEY_CURRENT_USER, registry_path.c_str(), KEY_SET_VALUE)
-      .DeleteKey(L"");
-
-  // Get the new group name.
-  const base::string16 group = base::UTF8ToUTF16(
-      base::FieldTrialList::FindFullName(kPreReadFieldTrialName));
-  if (group.empty())
-    return;
-
-  // Get variation params for the new group.
-  std::map<std::string, std::string> variation_params;
-  variations::GetVariationParams(kPreReadFieldTrialName, &variation_params);
-
-  // Open the registry key.
-  base::win::RegKey key(HKEY_CURRENT_USER, registry_path.c_str(),
-                        KEY_SET_VALUE);
-
-  // Write variation params in the registry.
-  for (const auto& variation_param : variation_params) {
-    if (!variation_param.second.empty()) {
-      if (key.WriteValue(base::UTF8ToUTF16(variation_param.first).c_str(), 1) !=
-          ERROR_SUCCESS) {
-        // Abort on failure to prevent the group name from being written in the
-        // registry if not all variation params have been written. No synthetic
-        // field trial is registered when there is no group name in the
-        // registry.
-        return;
-      }
-    }
-  }
-
-  // Write the new group name in the registry.
-  key.WriteValue(L"", group.c_str());
-}
-
-void RegisterPreReadSyntheticFieldTrial(
-    const base::string16& product_registry_path,
-    const RegisterPreReadSyntheticFieldTrialCallback&
-        register_synthetic_field_trial) {
-  DCHECK(!product_registry_path.empty());
-
-  const base::win::RegKey key(
-      HKEY_CURRENT_USER, GetPreReadRegistryPath(product_registry_path).c_str(),
-      KEY_QUERY_VALUE);
-  base::string16 group;
-  key.ReadValue(L"", &group);
-
-  if (!group.empty()) {
-    register_synthetic_field_trial.Run(kPreReadSyntheticFieldTrialName,
-                                       base::UTF16ToUTF8(group));
-  }
-}
-
-}  // namespace startup_metric_utils