Remove all code related to the PreRead field trial.

components/startup_metric_utils/common/pre_read_field_trial_utils_win.h

-// 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.
-
-#ifndef COMPONENTS_STARTUP_METRIC_UTILS_COMMON_PRE_READ_FIELD_TRIAL_UTILS_WIN_H_
-#define COMPONENTS_STARTUP_METRIC_UTILS_COMMON_PRE_READ_FIELD_TRIAL_UTILS_WIN_H_
-
-#include <string>
-
-#include "base/callback_forward.h"
-#include "base/strings/string16.h"
-
-// Utility functions to support the PreRead field trial. The PreRead field trial
-// changes the way DLLs are pre-read during startup.
-
-namespace startup_metric_utils {
-
-// Callback to register a synthetic field trial.
-using RegisterPreReadSyntheticFieldTrialCallback =
-    const base::Callback<bool(const std::string&, const std::string&)>;
-
-// The options controlled by the PreRead field trial.
-struct PreReadOptions {
-  // Pre-read DLLs explicitly.
-  bool pre_read : 1;
-
-  // Pre-read DLLs with a high thread priority.
-  bool high_priority : 1;
-
-  // Pre-read DLLs using the ::PrefetchVirtualMemory function, if available.
-  bool prefetch_virtual_memory : 1;
-};
-
-// Initializes DLL pre-reading options from the registry.
-// |product_registry_path| is the registry path under which the registry key for
-// this field trial resides.
-void InitializePreReadOptions(const base::string16& product_registry_path);
-
-// Returns the bitfield of the DLL pre-reading options to use for the current
-// process. InitializePreReadOptions() must have been called before this.
-PreReadOptions GetPreReadOptions();
-
-// Updates DLL pre-reading options in the registry with the latest info for the
-// next startup. |product_registry_path| is the registry path under which the
-// registry key for this field trial resides.
-void UpdatePreReadOptions(const base::string16& product_registry_path);
-
-// Registers a synthetic field trial with the PreRead group currently stored in
-// the registry. This must be done before the first metric log
-// (metrics::MetricsLog) is created. Otherwise, UMA metrics generated during
-// startup won't be correctly annotated. |product_registry_path| is the registry
-// path under which the key for this field trial resides.
-void RegisterPreReadSyntheticFieldTrial(
-    const base::string16& product_registry_path,
-    const RegisterPreReadSyntheticFieldTrialCallback&
-        register_synthetic_field_trial);
-
-}  // namespace startup_metric_utils
-
-#endif  // COMPONENTS_STARTUP_METRIC_UTILS_COMMON_PRE_READ_FIELD_TRIAL_UTILS_WIN_H_