Remove code related to the OnlyIfCold option of the PreRead field trial.

Experimental results show that the heuristic that was used to determine
whether a binary is warm isn't good enough.

BUG=547794

Review URL: https://codereview.chromium.org/1654823004

Cr-Commit-Position: refs/heads/master@{#373301}

chrome/BUILD.gn

@@ -534,7 +534,6 @@ if (is_win) {
     ]
     deps = [
       "//base",
-      "//components/startup_metric_utils/browser:lib",
     ]
   }
 }

chrome/app/file_pre_reader_win.cc

@@ -7,15 +7,13 @@
 #include <windows.h>
 #include <stdint.h>
 
-#include "base/debug/alias.h"
 #include "base/files/file.h"
 #include "base/files/memory_mapped_file.h"
 #include "base/logging.h"
 #include "base/scoped_native_library.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/win/pe_image.h"
 #include "base/win/windows_version.h"
-#include "components/startup_metric_utils/browser/startup_metric_utils.h"
 
 namespace {
 
@@ -104,30 +102,6 @@ void PreReadFile(const base::FilePath& file_path) {
   }
 }
 
-bool IsMemoryMappedFileWarm(const base::MemoryMappedFile& memory_mapped_file) {
-  base::ThreadRestrictions::AssertIOAllowed();
-  if (!memory_mapped_file.IsValid())
-    return false;
-
-  uint32_t initial_hard_fault_count = 0;
-  if (!startup_metric_utils::GetHardFaultCountForCurrentProcess(
-          &initial_hard_fault_count))
-    return false;
-
-  // Read a byte from the first page of the memory map.
-  const uint8_t dummy = *(memory_mapped_file.data());
-  base::debug::Alias(&dummy);
-
-  uint32_t final_hard_fault_count = 0;
-  if (!startup_metric_utils::GetHardFaultCountForCurrentProcess(
-          &final_hard_fault_count))
-    return false;
-
-  // Return true if reading a byte from the first page of the memory map
-  // generated a hard fault.
-  return initial_hard_fault_count == final_hard_fault_count;
-}
-
 void PreReadMemoryMappedFile(const base::MemoryMappedFile& memory_mapped_file,
                              const base::FilePath& file_path) {
   base::ThreadRestrictions::AssertIOAllowed();

chrome/app/file_pre_reader_win.h

@@ -19,11 +19,6 @@ class MemoryMappedFile;
 // pre-reading non-PE files is not supported.
 void PreReadFile(const base::FilePath& file_path);
 
-// Returns true if the first page of |memory_mapped_file| is warm. This function
-// must be called from a single-threaded process because it relies on the
-// process-wide hard fault counter. Returns false on failure.
-bool IsMemoryMappedFileWarm(const base::MemoryMappedFile& memory_mapped_file);
-
 // Reads |memory_mapped_file| to avoid touching the disk when the mapped file is
 // actually used. The function checks the Windows version to determine which
 // pre-reading mechanism to use. On Win8+, it uses ::PrefetchVirtualMemory. On

chrome/app/main_dll_loader_win.cc

@@ -75,17 +75,7 @@ HMODULE LoadModuleWithDirectory(const base::FilePath& module) {
           base::ThreadPriority::DISPLAY);
     }
 
-    if (pre_read_options.only_if_cold) {
-      base::MemoryMappedFile module_memory_map;
-      const bool map_initialize_success = module_memory_map.Initialize(module);
-      DCHECK(map_initialize_success);
-      if (!IsMemoryMappedFileWarm(module_memory_map)) {
-        if (pre_read_options.prefetch_virtual_memory)
-          PreReadMemoryMappedFile(module_memory_map, module);
-        else
-          PreReadFile(module);
-      }
-    } else if (pre_read_options.prefetch_virtual_memory) {
+    if (pre_read_options.prefetch_virtual_memory) {
       base::MemoryMappedFile module_memory_map;
       const bool map_initialize_success = module_memory_map.Initialize(module);
       DCHECK(map_initialize_success);

chrome/chrome_exe.gypi

@@ -513,7 +513,6 @@
           ],
           'dependencies': [
              '../base/base.gyp:base',
-             '../components/components.gyp:startup_metric_utils_browser',
           ],
         },
       ],

components/startup_metric_utils/common/pre_read_field_trial_utils_win.cc

@@ -31,7 +31,6 @@ const char kPreReadSyntheticFieldTrialName[] = "SyntheticPreRead";
 // name.
 const base::char16 kNoPreReadVariationName[] = L"NoPreRead";
 const base::char16 kHighPriorityVariationName[] = L"HighPriority";
-const base::char16 kOnlyIfColdVariationName[] = L"OnlyIfCold";
 const base::char16 kPrefetchVirtualMemoryVariationName[] =
     L"PrefetchVirtualMemory";
 const base::char16 kNoPrefetchArgumentVariationName[] = L"NoPrefetchArgument";
@@ -69,7 +68,6 @@ void InitializePreReadOptions(const base::string16& product_registry_path) {
   // 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.only_if_cold = ReadBool(key, kOnlyIfColdVariationName);
   g_pre_read_options.prefetch_virtual_memory =
       ReadBool(key, kPrefetchVirtualMemoryVariationName);
   g_pre_read_options.use_prefetch_argument =

components/startup_metric_utils/common/pre_read_field_trial_utils_win.h

@@ -27,9 +27,6 @@ struct PreReadOptions {
   // Pre-read DLLs with a high thread priority.
   bool high_priority;
 
-  // Pre-read DLLs only when they are cold.
-  bool only_if_cold;
-
   // Pre-read DLLs using the ::PrefetchVirtualMemory function, if available.
   bool prefetch_virtual_memory;