dart:io | Remove some unneeded global error save/restore pairs on Windows.

runtime/bin/file_win.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_WINDOWS)
 
 #include "bin/file.h"
 
 #include <fcntl.h>  // NOLINT
@@ skipping 307 matching lines @@
       FSCTL_GET_REPARSE_POINT,
       NULL,
       0,
       buffer,
       buffer_size,
       &received_bytes,
       NULL);
   if (result == 0) {
     DWORD error = GetLastError();
     CloseHandle(dir_handle);
+    SetLastError(error);
     free(buffer);
-    SetLastError(error);
     return NULL;
   }
   if (CloseHandle(dir_handle) == 0) {
-    DWORD error = GetLastError();
     free(buffer);
-    SetLastError(error);
     return NULL;
   }
 
   wchar_t* target;
   size_t target_offset;
   size_t target_length;
   if (buffer->ReparseTag == IO_REPARSE_TAG_MOUNT_POINT) {
     target = buffer->MountPointReparseBuffer.PathBuffer;
     target_offset = buffer->MountPointReparseBuffer.SubstituteNameOffset;
     target_length = buffer->MountPointReparseBuffer.SubstituteNameLength;
@@ skipping 25 matching lines @@
                                         NULL);
   char* utf8_target = reinterpret_cast<char*>(malloc(utf8_length + 1));
   if (0 == WideCharToMultiByte(CP_UTF8,
                                0,
                                target,
                                target_length,
                                utf8_target,
                                utf8_length,
                                NULL,
                                NULL)) {
-    DWORD error = GetLastError();
     free(buffer);
     free(utf8_target);
-    SetLastError(error);
     return NULL;
   }
   utf8_target[utf8_length] = '\0';
   free(buffer);
   return utf8_target;
 }
 
 
 time_t File::LastModified(const char* name) {
   struct _stat st;
@@ skipping 129 matching lines @@
     const wchar_t* wide_name = StringUtils::Utf8ToWide(file_names[i]);
     HANDLE file_handle = CreateFileW(
         wide_name,
         0,
         FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
         NULL,
         OPEN_EXISTING,
         FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OPEN_REPARSE_POINT,
         NULL);
     if (file_handle == INVALID_HANDLE_VALUE) {
-      DWORD error = GetLastError();
       free(const_cast<wchar_t*>(wide_name));
-      SetLastError(error);
       return File::kError;
     }
     free(const_cast<wchar_t*>(wide_name));
     int result = GetFileInformationByHandle(file_handle, &file_info[i]);
     if (result == 0) {
       DWORD error = GetLastError();
       CloseHandle(file_handle);
       SetLastError(error);
       return File::kError;
     }
     if (CloseHandle(file_handle) == 0) {
       return File::kError;
     }
   }
   if (file_info[0].dwVolumeSerialNumber == file_info[1].dwVolumeSerialNumber &&
       file_info[0].nFileIndexHigh == file_info[1].nFileIndexHigh &&
       file_info[0].nFileIndexLow == file_info[1].nFileIndexLow) {
     return kIdentical;
   } else {
     return kDifferent;
   }
 }
 
 #endif  // defined(TARGET_OS_WINDOWS)