Revert of Reland 2:Geolocation: move from content/browser to device/

content/browser/geolocation/wifi_data_provider_win.cc

Index: content/browser/geolocation/wifi_data_provider_win.cc
diff --git a/content/browser/geolocation/wifi_data_provider_win.cc b/content/browser/geolocation/wifi_data_provider_win.cc
new file mode 100644
index 0000000000000000000000000000000000000000..c5eca3d6f20298508351650a8c204bec0f14c337
--- /dev/null
+++ b/content/browser/geolocation/wifi_data_provider_win.cc
@@ -0,0 +1,643 @@
+// Copyright (c) 2010 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.
+
+// Windows Vista uses the Native Wifi (WLAN) API for accessing WiFi cards. See
+// http://msdn.microsoft.com/en-us/library/ms705945(VS.85).aspx. Windows XP
+// Service Pack 3 (and Windows XP Service Pack 2, if upgraded with a hot fix)
+// also support a limited version of the WLAN API. See
+// http://msdn.microsoft.com/en-us/library/bb204766.aspx. The WLAN API uses
+// wlanapi.h, which is not part of the SDK used by Gears, so is replicated
+// locally using data from the MSDN.
+//
+// Windows XP from Service Pack 2 onwards supports the Wireless Zero
+// Configuration (WZC) programming interface. See
+// http://msdn.microsoft.com/en-us/library/ms706587(VS.85).aspx.
+//
+// The MSDN recommends that one use the WLAN API where available, and WZC
+// otherwise.
+//
+// However, it seems that WZC fails for some wireless cards. Also, WLAN seems
+// not to work on XP SP3. So we use WLAN on Vista, and use NDIS directly
+// otherwise.
+
+#include "content/browser/geolocation/wifi_data_provider_win.h"
+
+#include <windows.h>
+#include <winioctl.h>
+#include <wlanapi.h>
+
+#include "base/memory/free_deleter.h"
+#include "base/metrics/histogram.h"
+#include "base/strings/utf_string_conversions.h"
+#include "base/win/windows_version.h"
+#include "content/browser/geolocation/wifi_data_provider_common.h"
+#include "content/browser/geolocation/wifi_data_provider_common_win.h"
+#include "content/browser/geolocation/wifi_data_provider_manager.h"
+
+// Taken from ndis.h for WinCE.
+#define NDIS_STATUS_INVALID_LENGTH   ((NDIS_STATUS)0xC0010014L)
+#define NDIS_STATUS_BUFFER_TOO_SHORT ((NDIS_STATUS)0xC0010016L)
+
+namespace content {
+namespace {
+// The limits on the size of the buffer used for the OID query.
+const int kInitialBufferSize = 2 << 12;  // Good for about 50 APs.
+const int kMaximumBufferSize = 2 << 20;  // 2MB
+
+// Length for generic string buffers passed to Windows APIs.
+const int kStringLength = 512;
+
+// The time periods, in milliseconds, between successive polls of the wifi data.
+const int kDefaultPollingInterval = 10000;  // 10s
+const int kNoChangePollingInterval = 120000;  // 2 mins
+const int kTwoNoChangePollingInterval = 600000;  // 10 mins
+const int kNoWifiPollingIntervalMilliseconds = 20 * 1000; // 20s
+
+// WlanOpenHandle
+typedef DWORD (WINAPI* WlanOpenHandleFunction)(DWORD dwClientVersion,
+                                               PVOID pReserved,
+                                               PDWORD pdwNegotiatedVersion,
+                                               PHANDLE phClientHandle);
+
+// WlanEnumInterfaces
+typedef DWORD (WINAPI* WlanEnumInterfacesFunction)(
+    HANDLE hClientHandle,
+    PVOID pReserved,
+    PWLAN_INTERFACE_INFO_LIST* ppInterfaceList);
+
+// WlanGetNetworkBssList
+typedef DWORD (WINAPI* WlanGetNetworkBssListFunction)(
+    HANDLE hClientHandle,
+    const GUID* pInterfaceGuid,
+    const  PDOT11_SSID pDot11Ssid,
+    DOT11_BSS_TYPE dot11BssType,
+    BOOL bSecurityEnabled,
+    PVOID pReserved,
+    PWLAN_BSS_LIST* ppWlanBssList
+);
+
+// WlanFreeMemory
+typedef VOID (WINAPI* WlanFreeMemoryFunction)(PVOID pMemory);
+
+// WlanCloseHandle
+typedef DWORD (WINAPI* WlanCloseHandleFunction)(HANDLE hClientHandle,
+                                                PVOID pReserved);
+
+
+// Local classes and functions
+class WindowsWlanApi : public WifiDataProviderCommon::WlanApiInterface {
+ public:
+  ~WindowsWlanApi() override;
+  // Factory function. Will return NULL if this API is unavailable.
+  static WindowsWlanApi* Create();
+
+  // WlanApiInterface
+  bool GetAccessPointData(WifiData::AccessPointDataSet* data) override;
+
+ private:
+  // Takes ownership of the library handle.
+  explicit WindowsWlanApi(HINSTANCE library);
+
+  // Loads the required functions from the DLL.
+  void GetWLANFunctions(HINSTANCE wlan_library);
+  int GetInterfaceDataWLAN(HANDLE wlan_handle,
+                           const GUID& interface_id,
+                           WifiData::AccessPointDataSet* data);
+
+  // Logs number of detected wlan interfaces.
+  static void LogWlanInterfaceCount(int count);
+
+  // Handle to the wlanapi.dll library.
+  HINSTANCE library_;
+
+  // Function pointers for WLAN
+  WlanOpenHandleFunction WlanOpenHandle_function_;
+  WlanEnumInterfacesFunction WlanEnumInterfaces_function_;
+  WlanGetNetworkBssListFunction WlanGetNetworkBssList_function_;
+  WlanFreeMemoryFunction WlanFreeMemory_function_;
+  WlanCloseHandleFunction WlanCloseHandle_function_;
+};
+
+class WindowsNdisApi : public WifiDataProviderCommon::WlanApiInterface {
+ public:
+  ~WindowsNdisApi() override;
+  static WindowsNdisApi* Create();
+
+  // WlanApiInterface
+  bool GetAccessPointData(WifiData::AccessPointDataSet* data) override;
+
+ private:
+  static bool GetInterfacesNDIS(
+      std::vector<base::string16>* interface_service_names_out);
+
+  // Swaps in content of the vector passed
+  explicit WindowsNdisApi(std::vector<base::string16>* interface_service_names);
+
+  bool GetInterfaceDataNDIS(HANDLE adapter_handle,
+                            WifiData::AccessPointDataSet* data);
+  // NDIS variables.
+  std::vector<base::string16> interface_service_names_;
+
+  // Remembers scan result buffer size across calls.
+  int oid_buffer_size_;
+};
+
+// Extracts data for an access point and converts to Gears format.
+bool GetNetworkData(const WLAN_BSS_ENTRY& bss_entry,
+                    AccessPointData* access_point_data);
+bool UndefineDosDevice(const base::string16& device_name);
+bool DefineDosDeviceIfNotExists(const base::string16& device_name);
+HANDLE GetFileHandle(const base::string16& device_name);
+// Makes the OID query and returns a Windows API error code.
+int PerformQuery(HANDLE adapter_handle,
+                 BYTE* buffer,
+                 DWORD buffer_size,
+                 DWORD* bytes_out);
+bool ResizeBuffer(int requested_size,
+                  std::unique_ptr<BYTE, base::FreeDeleter>* buffer);
+// Gets the system directory and appends a trailing slash if not already
+// present.
+bool GetSystemDirectory(base::string16* path);
+}  // namespace
+
+WifiDataProvider* WifiDataProviderManager::DefaultFactoryFunction() {
+  return new WifiDataProviderWin();
+}
+
+WifiDataProviderWin::WifiDataProviderWin() {
+}
+
+WifiDataProviderWin::~WifiDataProviderWin() {
+}
+
+WifiDataProviderCommon::WlanApiInterface* WifiDataProviderWin::NewWlanApi() {
+  // Use the WLAN interface if we're on Vista and if it's available. Otherwise,
+  // use NDIS.
+  WlanApiInterface* api = WindowsWlanApi::Create();
+  if (api) {
+    return api;
+  }
+  return WindowsNdisApi::Create();
+}
+
+WifiPollingPolicy* WifiDataProviderWin::NewPollingPolicy() {
+  return new GenericWifiPollingPolicy<kDefaultPollingInterval,
+                                      kNoChangePollingInterval,
+                                      kTwoNoChangePollingInterval,
+                                      kNoWifiPollingIntervalMilliseconds>;
+}
+
+// Local classes and functions
+namespace {
+
+// WindowsWlanApi
+WindowsWlanApi::WindowsWlanApi(HINSTANCE library)
+    : library_(library) {
+  GetWLANFunctions(library_);
+}
+
+WindowsWlanApi::~WindowsWlanApi() {
+  FreeLibrary(library_);
+}
+
+WindowsWlanApi* WindowsWlanApi::Create() {
+  if (base::win::GetVersion() < base::win::VERSION_VISTA)
+    return NULL;
+  // We use an absolute path to load the DLL to avoid DLL preloading attacks.
+  base::string16 system_directory;
+  if (!GetSystemDirectory(&system_directory)) {
+    return NULL;
+  }
+  DCHECK(!system_directory.empty());
+  base::string16 dll_path = system_directory + L"wlanapi.dll";
+  HINSTANCE library = LoadLibraryEx(dll_path.c_str(),
+                                    NULL,
+                                    LOAD_WITH_ALTERED_SEARCH_PATH);
+  if (!library) {
+    return NULL;
+  }
+  return new WindowsWlanApi(library);
+}
+
+void WindowsWlanApi::GetWLANFunctions(HINSTANCE wlan_library) {
+  DCHECK(wlan_library);
+  WlanOpenHandle_function_ = reinterpret_cast<WlanOpenHandleFunction>(
+      GetProcAddress(wlan_library, "WlanOpenHandle"));
+  WlanEnumInterfaces_function_ = reinterpret_cast<WlanEnumInterfacesFunction>(
+      GetProcAddress(wlan_library, "WlanEnumInterfaces"));
+  WlanGetNetworkBssList_function_ =
+      reinterpret_cast<WlanGetNetworkBssListFunction>(
+      GetProcAddress(wlan_library, "WlanGetNetworkBssList"));
+  WlanFreeMemory_function_ = reinterpret_cast<WlanFreeMemoryFunction>(
+      GetProcAddress(wlan_library, "WlanFreeMemory"));
+  WlanCloseHandle_function_ = reinterpret_cast<WlanCloseHandleFunction>(
+      GetProcAddress(wlan_library, "WlanCloseHandle"));
+  DCHECK(WlanOpenHandle_function_ &&
+         WlanEnumInterfaces_function_ &&
+         WlanGetNetworkBssList_function_ &&
+         WlanFreeMemory_function_ &&
+         WlanCloseHandle_function_);
+}
+
+void WindowsWlanApi::LogWlanInterfaceCount(int count) {
+  UMA_HISTOGRAM_CUSTOM_COUNTS(
+      "Net.Wifi.InterfaceCount",
+      count,
+      1,
+      5,
+      6);
+}
+
+bool WindowsWlanApi::GetAccessPointData(
+    WifiData::AccessPointDataSet* data) {
+  DCHECK(data);
+
+  // Get the handle to the WLAN API.
+  DWORD negotiated_version;
+  HANDLE wlan_handle = NULL;
+  // We could be executing on either Windows XP or Windows Vista, so use the
+  // lower version of the client WLAN API. It seems that the negotiated version
+  // is the Vista version irrespective of what we pass!
+  static const int kXpWlanClientVersion = 1;
+  if ((*WlanOpenHandle_function_)(kXpWlanClientVersion,
+                                  NULL,
+                                  &negotiated_version,
+                                  &wlan_handle) != ERROR_SUCCESS) {
+    LogWlanInterfaceCount(0);
+    return false;
+  }
+  DCHECK(wlan_handle);
+
+  // Get the list of interfaces. WlanEnumInterfaces allocates interface_list.
+  WLAN_INTERFACE_INFO_LIST* interface_list = NULL;
+  if ((*WlanEnumInterfaces_function_)(wlan_handle, NULL, &interface_list) !=
+      ERROR_SUCCESS) {
+    LogWlanInterfaceCount(0);
+    return false;
+  }
+  DCHECK(interface_list);
+
+  LogWlanInterfaceCount(interface_list->dwNumberOfItems);
+
+  // Go through the list of interfaces and get the data for each.
+  for (int i = 0; i < static_cast<int>(interface_list->dwNumberOfItems); ++i) {
+    // Skip any interface that is midway through association; the
+    // WlanGetNetworkBssList function call is known to hang indefinitely
+    // when it's in this state. http://crbug.com/39300
+    if (interface_list->InterfaceInfo[i].isState ==
+        wlan_interface_state_associating) {
+      LOG(WARNING) << "Skipping wifi scan on adapter " << i << " ("
+                   << interface_list->InterfaceInfo[i].strInterfaceDescription
+                   << ") in 'associating' state. Repeated occurrences "
+                      "indicates a non-responding adapter.";
+      continue;
+    }
+    GetInterfaceDataWLAN(wlan_handle,
+                         interface_list->InterfaceInfo[i].InterfaceGuid,
+                         data);
+  }
+
+  // Free interface_list.
+  (*WlanFreeMemory_function_)(interface_list);
+
+  // Close the handle.
+  if ((*WlanCloseHandle_function_)(wlan_handle, NULL) != ERROR_SUCCESS) {
+    return false;
+  }
+
+  return true;
+}
+
+// Appends the data for a single interface to the data vector. Returns the
+// number of access points found, or -1 on error.
+int WindowsWlanApi::GetInterfaceDataWLAN(
+    const HANDLE wlan_handle,
+    const GUID& interface_id,
+    WifiData::AccessPointDataSet* data) {
+  DCHECK(data);
+
+  const base::TimeTicks start_time = base::TimeTicks::Now();
+
+  // WlanGetNetworkBssList allocates bss_list.
+  WLAN_BSS_LIST* bss_list = NULL;
+  if ((*WlanGetNetworkBssList_function_)(wlan_handle,
+                                         &interface_id,
+                                         NULL,   // Use all SSIDs.
+                                         dot11_BSS_type_any,
+                                         false,  // bSecurityEnabled - unused
+                                         NULL,   // reserved
+                                         &bss_list) != ERROR_SUCCESS) {
+    return -1;
+  }
+  // According to http://www.attnetclient.com/kb/questions.php?questionid=75
+  // WlanGetNetworkBssList can sometimes return success, but leave the bss
+  // list as NULL.
+  if (!bss_list)
+    return -1;
+
+  const base::TimeDelta duration = base::TimeTicks::Now() - start_time;
+
+  UMA_HISTOGRAM_CUSTOM_TIMES(
+      "Net.Wifi.ScanLatency",
+      duration,
+      base::TimeDelta::FromMilliseconds(1),
+      base::TimeDelta::FromMinutes(1),
+      100);
+
+
+  int found = 0;
+  for (int i = 0; i < static_cast<int>(bss_list->dwNumberOfItems); ++i) {
+    AccessPointData access_point_data;
+    if (GetNetworkData(bss_list->wlanBssEntries[i], &access_point_data)) {
+      ++found;
+      data->insert(access_point_data);
+    }
+  }
+
+  (*WlanFreeMemory_function_)(bss_list);
+
+  return found;
+}
+
+// WindowsNdisApi
+WindowsNdisApi::WindowsNdisApi(
+    std::vector<base::string16>* interface_service_names)
+    : oid_buffer_size_(kInitialBufferSize) {
+  DCHECK(!interface_service_names->empty());
+  interface_service_names_.swap(*interface_service_names);
+}
+
+WindowsNdisApi::~WindowsNdisApi() {
+}
+
+WindowsNdisApi* WindowsNdisApi::Create() {
+  std::vector<base::string16> interface_service_names;
+  if (GetInterfacesNDIS(&interface_service_names)) {
+    return new WindowsNdisApi(&interface_service_names);
+  }
+  return NULL;
+}
+
+bool WindowsNdisApi::GetAccessPointData(WifiData::AccessPointDataSet* data) {
+  DCHECK(data);
+  int interfaces_failed = 0;
+  int interfaces_succeeded = 0;
+
+  for (int i = 0; i < static_cast<int>(interface_service_names_.size()); ++i) {
+    // First, check that we have a DOS device for this adapter.
+    if (!DefineDosDeviceIfNotExists(interface_service_names_[i])) {
+      continue;
+    }
+
+    // Get the handle to the device. This will fail if the named device is not
+    // valid.
+    HANDLE adapter_handle = GetFileHandle(interface_service_names_[i]);
+    if (adapter_handle == INVALID_HANDLE_VALUE) {
+      continue;
+    }
+
+    // Get the data.
+    if (GetInterfaceDataNDIS(adapter_handle, data)) {
+      ++interfaces_succeeded;
+    } else {
+      ++interfaces_failed;
+    }
+
+    // Clean up.
+    CloseHandle(adapter_handle);
+    UndefineDosDevice(interface_service_names_[i]);
+  }
+
+  // Return true if at least one interface succeeded, or at the very least none
+  // failed.
+  return interfaces_succeeded > 0 || interfaces_failed == 0;
+}
+
+bool WindowsNdisApi::GetInterfacesNDIS(
+    std::vector<base::string16>* interface_service_names_out) {
+  HKEY network_cards_key = NULL;
+  if (RegOpenKeyEx(
+      HKEY_LOCAL_MACHINE,
+      L"Software\\Microsoft\\Windows NT\\CurrentVersion\\NetworkCards",
+      0,
+      KEY_READ,
+      &network_cards_key) != ERROR_SUCCESS) {
+    return false;
+  }
+  DCHECK(network_cards_key);
+
+  for (int i = 0; ; ++i) {
+    TCHAR name[kStringLength];
+    DWORD name_size = kStringLength;
+    FILETIME time;
+    if (RegEnumKeyEx(network_cards_key,
+                     i,
+                     name,
+                     &name_size,
+                     NULL,
+                     NULL,
+                     NULL,
+                     &time) != ERROR_SUCCESS) {
+      break;
+    }
+    HKEY hardware_key = NULL;
+    if (RegOpenKeyEx(network_cards_key, name, 0, KEY_READ, &hardware_key) !=
+        ERROR_SUCCESS) {
+      break;
+    }
+    DCHECK(hardware_key);
+
+    TCHAR service_name[kStringLength];
+    DWORD service_name_size = kStringLength;
+    DWORD type = 0;
+    if (RegQueryValueEx(hardware_key,
+                        L"ServiceName",
+                        NULL,
+                        &type,
+                        reinterpret_cast<LPBYTE>(service_name),
+                        &service_name_size) == ERROR_SUCCESS) {
+      interface_service_names_out->push_back(service_name);
+    }
+    RegCloseKey(hardware_key);
+  }
+
+  RegCloseKey(network_cards_key);
+  return true;
+}
+
+
+bool WindowsNdisApi::GetInterfaceDataNDIS(HANDLE adapter_handle,
+                                          WifiData::AccessPointDataSet* data) {
+  DCHECK(data);
+
+  std::unique_ptr<BYTE, base::FreeDeleter> buffer(
+      static_cast<BYTE*>(malloc(oid_buffer_size_)));
+  if (buffer == NULL) {
+    return false;
+  }
+
+  DWORD bytes_out;
+  int result;
+
+  while (true) {
+    bytes_out = 0;
+    result = PerformQuery(adapter_handle, buffer.get(),
+                          oid_buffer_size_, &bytes_out);
+    if (result == ERROR_GEN_FAILURE ||  // Returned by some Intel cards.
+        result == ERROR_INSUFFICIENT_BUFFER ||
+        result == ERROR_MORE_DATA ||
+        result == NDIS_STATUS_INVALID_LENGTH ||
+        result == NDIS_STATUS_BUFFER_TOO_SHORT) {
+      // The buffer we supplied is too small, so increase it. bytes_out should
+      // provide the required buffer size, but this is not always the case.
+      if (bytes_out > static_cast<DWORD>(oid_buffer_size_)) {
+        oid_buffer_size_ = bytes_out;
+      } else {
+        oid_buffer_size_ *= 2;
+      }
+      if (!ResizeBuffer(oid_buffer_size_, &buffer)) {
+        oid_buffer_size_ = kInitialBufferSize;  // Reset for next time.
+        return false;
+      }
+    } else {
+      // The buffer is not too small.
+      break;
+    }
+  }
+  DCHECK(buffer.get());
+
+  if (result == ERROR_SUCCESS) {
+    NDIS_802_11_BSSID_LIST* bssid_list =
+        reinterpret_cast<NDIS_802_11_BSSID_LIST*>(buffer.get());
+    GetDataFromBssIdList(*bssid_list, oid_buffer_size_, data);
+  }
+
+  return true;
+}
+
+bool GetNetworkData(const WLAN_BSS_ENTRY& bss_entry,
+                    AccessPointData* access_point_data) {
+  // Currently we get only MAC address, signal strength and SSID.
+  DCHECK(access_point_data);
+  access_point_data->mac_address = MacAddressAsString16(bss_entry.dot11Bssid);
+  access_point_data->radio_signal_strength = bss_entry.lRssi;
+  // bss_entry.dot11Ssid.ucSSID is not null-terminated.
+  base::UTF8ToUTF16(reinterpret_cast<const char*>(bss_entry.dot11Ssid.ucSSID),
+                    static_cast<ULONG>(bss_entry.dot11Ssid.uSSIDLength),
+                    &access_point_data->ssid);
+  // TODO(steveblock): Is it possible to get the following?
+  // access_point_data->signal_to_noise
+  // access_point_data->age
+  // access_point_data->channel
+  return true;
+}
+
+bool UndefineDosDevice(const base::string16& device_name) {
+  // We remove only the mapping we use, that is \Device\<device_name>.
+  base::string16 target_path = L"\\Device\\" + device_name;
+  return DefineDosDevice(
+      DDD_RAW_TARGET_PATH | DDD_REMOVE_DEFINITION | DDD_EXACT_MATCH_ON_REMOVE,
+      device_name.c_str(),
+      target_path.c_str()) == TRUE;
+}
+
+bool DefineDosDeviceIfNotExists(const base::string16& device_name) {
+  // We create a DOS device name for the device at \Device\<device_name>.
+  base::string16 target_path = L"\\Device\\" + device_name;
+
+  TCHAR target[kStringLength];
+  if (QueryDosDevice(device_name.c_str(), target, kStringLength) > 0 &&
+      target_path.compare(target) == 0) {
+    // Device already exists.
+    return true;
+  }
+
+  if (GetLastError() != ERROR_FILE_NOT_FOUND) {
+    return false;
+  }
+
+  if (!DefineDosDevice(DDD_RAW_TARGET_PATH,
+                       device_name.c_str(),
+                       target_path.c_str())) {
+    return false;
+  }
+
+  // Check that the device is really there.
+  return QueryDosDevice(device_name.c_str(), target, kStringLength) > 0 &&
+      target_path.compare(target) == 0;
+}
+
+HANDLE GetFileHandle(const base::string16& device_name) {
+  // We access a device with DOS path \Device\<device_name> at
+  // \\.\<device_name>.
+  base::string16 formatted_device_name = L"\\\\.\\" + device_name;
+
+  return CreateFile(formatted_device_name.c_str(),
+                    GENERIC_READ,
+                    FILE_SHARE_READ | FILE_SHARE_WRITE,  // share mode
+                    0,  // security attributes
+                    OPEN_EXISTING,
+                    0,  // flags and attributes
+                    INVALID_HANDLE_VALUE);
+}
+
+int PerformQuery(HANDLE adapter_handle,
+                 BYTE* buffer,
+                 DWORD buffer_size,
+                 DWORD* bytes_out) {
+  DWORD oid = OID_802_11_BSSID_LIST;
+  if (!DeviceIoControl(adapter_handle,
+                       IOCTL_NDIS_QUERY_GLOBAL_STATS,
+                       &oid,
+                       sizeof(oid),
+                       buffer,
+                       buffer_size,
+                       bytes_out,
+                       NULL)) {
+    return GetLastError();
+  }
+  return ERROR_SUCCESS;
+}
+
+bool ResizeBuffer(int requested_size,
+                  std::unique_ptr<BYTE, base::FreeDeleter>* buffer) {
+  DCHECK_GT(requested_size, 0);
+  DCHECK(buffer);
+  if (requested_size > kMaximumBufferSize) {
+    buffer->reset();
+    return false;
+  }
+
+  buffer->reset(reinterpret_cast<BYTE*>(
+      realloc(buffer->release(), requested_size)));
+  return buffer != NULL;
+}
+
+bool GetSystemDirectory(base::string16* path) {
+  DCHECK(path);
+  // Return value includes terminating NULL.
+  int buffer_size = ::GetSystemDirectory(NULL, 0);
+  if (buffer_size == 0) {
+    return false;
+  }
+  std::unique_ptr<base::char16[]> buffer(new base::char16[buffer_size]);
+
+  // Return value excludes terminating NULL.
+  int characters_written = ::GetSystemDirectory(buffer.get(), buffer_size);
+  if (characters_written == 0) {
+    return false;
+  }
+  DCHECK_EQ(buffer_size - 1, characters_written);
+
+  path->assign(buffer.get(), characters_written);
+
+  if (*path->rbegin() != L'\\') {
+    path->append(L"\\");
+  }
+  DCHECK_EQ(L'\\', *path->rbegin());
+  return true;
+}
+}  // namespace
+
+}  // namespace content