Remove code related to the PreReadChromeChildInBrowser field trial.

This field trial has expired.

BUG=557984

Review-Url: https://codereview.chromium.org/2286903002
Cr-Commit-Position: refs/heads/master@{#415683}

chrome/app/main_dll_loader_win.cc

@@ -62,14 +62,9 @@ HMODULE LoadModuleWithDirectory(const base::FilePath& module) {
       startup_metric_utils::GetPreReadOptions();
 
   // If enabled by the PreRead field trial, pre-read the binary to avoid a lot
-  // of random IO. Don't pre-read the binary if it is chrome_child.dll and the
-  // |pre_read_chrome_child_in_browser| option is enabled; the binary should
-  // already have been pre-read by the browser process in that case.
-  if (pre_read_options.pre_read &&
-      (!pre_read_options.pre_read_chrome_child_in_browser ||
-       module.BaseName().value() != installer::kChromeChildDll)) {
+  // of random IO.
+  if (pre_read_options.pre_read)
     PreReadFile(module, pre_read_options);
-  }
 
   return ::LoadLibraryExW(module.value().c_str(), nullptr,
                           LOAD_WITH_ALTERED_SEARCH_PATH);

chrome/browser/chrome_browser_main.cc

@@ -200,7 +200,6 @@
 #include "base/trace_event/trace_event_etw_export_win.h"
 #include "base/win/win_util.h"
 #include "base/win/windows_version.h"
-#include "chrome/app/file_pre_reader_win.h"
 #include "chrome/browser/chrome_browser_main_win.h"
 #include "chrome/browser/component_updater/sw_reporter_installer_win.h"
 #include "chrome/browser/downgrade/user_data_downgrade.h"
@@ -213,7 +212,6 @@
 #include "chrome/installer/util/browser_distribution.h"
 #include "chrome/installer/util/helper.h"
 #include "chrome/installer/util/install_util.h"
-#include "chrome/installer/util/module_util_win.h"
 #include "chrome/installer/util/shell_util.h"
 #include "components/startup_metric_utils/common/pre_read_field_trial_utils_win.h"
 #include "ui/base/l10n/l10n_util_win.h"
@@ -1551,18 +1549,6 @@ int ChromeBrowserMainParts::PreMainMessageLoopRunImpl() {
   const base::TimeTicks start_time_step1 = base::TimeTicks::Now();
 
 #if defined(OS_WIN)
-  // Pre-read chrome_child.dll.
-  const startup_metric_utils::PreReadOptions pre_read_options =
-      startup_metric_utils::GetPreReadOptions();
-  if (pre_read_options.pre_read &&
-      pre_read_options.pre_read_chrome_child_in_browser) {
-    BrowserThread::PostTask(
-        BrowserThread::FILE_USER_BLOCKING, FROM_HERE,
-        base::Bind(&PreReadFile,
-                   installer::GetModulePath(installer::kChromeChildDll),
-                   pre_read_options));
-  }
-
   // Windows parental controls calls can be slow, so we do an early init here
   // that calculates this value off of the UI thread.
   IncognitoModePrefs::InitializePlatformParentalControls();

components/startup_metric_utils/common/pre_read_field_trial_utils_win.cc

@@ -33,8 +33,6 @@ const base::char16 kNoPreReadVariationName[] = L"NoPreRead";
 const base::char16 kHighPriorityVariationName[] = L"HighPriority";
 const base::char16 kPrefetchVirtualMemoryVariationName[] =
     L"PrefetchVirtualMemory";
-const base::char16 kPreReadChromeChildInBrowser[] =
-    L"PreReadChromeChildInBrowser";
 
 // Registry key in which the PreRead field trial group is stored.
 const base::char16 kPreReadFieldTrialRegistryKey[] = L"\\PreReadFieldTrial";
@@ -77,8 +75,6 @@ void InitializePreReadOptions(const base::string16& product_registry_path) {
   g_pre_read_options.high_priority = ReadBool(key, kHighPriorityVariationName);
   g_pre_read_options.prefetch_virtual_memory =
       ReadBool(key, kPrefetchVirtualMemoryVariationName);
-  g_pre_read_options.pre_read_chrome_child_in_browser =
-      ReadBool(key, kPreReadChromeChildInBrowser);
 }
 
 PreReadOptions GetPreReadOptions() {

components/startup_metric_utils/common/pre_read_field_trial_utils_win.h

@@ -29,10 +29,6 @@ struct PreReadOptions {
 
   // 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.

testing/variations/fieldtrial_testing_config_win.json

@@ -324,20 +324,6 @@
             "group_name": "Enabled"
         }
     ],
-    "PreRead": [
-        {
-            "group_name": "NoPrefetchArgument2",
-            "params": {
-                "NoPrefetchArgument": "true"
-            }
-        },
-        {
-            "group_name": "PreReadChromeChildInBrowser",
-            "params": {
-                "PreReadChromeChildInBrowser": "true"
-            }
-        }
-    ],
     "PreconnectMore": [
         {
             "enable_features": [