Remove code related to the PreReadChromeChildInBrowser 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"
@@ skipping 11 matching lines @@
 // 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;
-
-  // Pre-read chrome_child.dll in the browser process and not in child
-  // processes.
-  bool pre_read_chrome_child_in_browser : 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_