Revert of Transform ImagePreReader into PreReadFile.

chrome/app/file_pre_reader_win.cc

-// Copyright (c) 2012 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 "chrome/app/file_pre_reader_win.h"
-
-#include <windows.h>
-
-#include "base/files/file.h"
-#include "base/files/memory_mapped_file.h"
-#include "base/logging.h"
-#include "base/threading/thread_restrictions.h"
-#include "base/win/windows_version.h"
-
-namespace {
-
-// A helper function to touch all pages in the range
-// [base_addr, base_addr + length).
-void TouchPagesInRange(const void* base_addr, size_t length) {
-  DCHECK(base_addr);
-  DCHECK_GT(length, static_cast<size_t>(0));
-
-  // Get the system info so we know the page size. Also, make sure we use a
-  // non-zero value for the page size; GetSystemInfo() is hookable/patchable,
-  // and you never know what shenanigans someone could get up to.
-  SYSTEM_INFO system_info = {};
-  ::GetSystemInfo(&system_info);
-  if (system_info.dwPageSize == 0)
-    system_info.dwPageSize = 4096;
-
-  // We don't want to read outside the byte range (which could trigger an
-  // access violation), so let's figure out the exact locations of the first
-  // and final bytes we want to read.
-  volatile uint8_t const* touch_ptr =
-      reinterpret_cast<uint8_t const*>(base_addr);
-  volatile uint8_t const* final_touch_ptr = touch_ptr + length - 1;
-
-  // Read the memory in the range [touch_ptr, final_touch_ptr] with a stride
-  // of the system page size, to ensure that it's been paged in.
-  uint8_t dummy;
-  for (; touch_ptr < final_touch_ptr; touch_ptr += system_info.dwPageSize)
-    dummy = *touch_ptr;
-  dummy = *final_touch_ptr;
-}
-
-}  // namespace
-
-bool PreReadFile(const base::FilePath& file_path, int step_size) {
-  DCHECK_GT(step_size, 0);
-  base::ThreadRestrictions::AssertIOAllowed();
-
-  if (base::win::GetVersion() > base::win::VERSION_XP) {
-    // Vista+ branch. On these OSes, the forced reads through the DLL actually
-    // slows warm starts. The solution is to sequentially read file contents.
-    base::File file(file_path, base::File::FLAG_OPEN | base::File::FLAG_READ |
-                                   base::File::FLAG_SEQUENTIAL_SCAN);
-    if (!file.IsValid())
-      return false;
-
-    char* buffer = reinterpret_cast<char*>(::VirtualAlloc(
-        nullptr, static_cast<DWORD>(step_size), MEM_COMMIT, PAGE_READWRITE));
-    if (!buffer)
-      return false;
-
-    while (file.ReadAtCurrentPos(buffer, step_size) > 0) {}
-
-    ::VirtualFree(buffer, 0, MEM_RELEASE);
-  } else {
-    // WinXP branch. Here, reading the DLL from disk doesn't do what we want so
-    // instead we pull the pages into memory and touch pages at a stride. We use
-    // the system's page size as the stride, ignoring the passed in step_size,
-    // to make sure each page in the range is touched.
-    base::MemoryMappedFile file_memory_map;
-    if (!file_memory_map.Initialize(file_path))
-      return false;
-    TouchPagesInRange(file_memory_map.data(), file_memory_map.length());
-  }
-
-  return true;
-}