LZMA: Unconditionally flush output files after unmapping.

BUG=933975,1069116
R=etiennep@chromium.org

Change-Id: I294eba49176369fe06f541e681b7fee84aba48bd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2146548
Commit-Queue: Greg Thompson <grt@chromium.org>
Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
Reviewed-by: Etienne Pierre-Doray <etiennep@chromium.org>
Auto-Submit: Greg Thompson <grt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#758876}

chrome/installer/util/lzma_util.cc

@@ -18,7 +18,6 @@
 #include "base/logging.h"
 #include "base/optional.h"
 #include "base/strings/utf_string_conversions.h"
-#include "base/win/windows_version.h"
 
 extern "C" {
 #include "third_party/lzma_sdk/7z.h"
@@ -370,12 +369,12 @@ UnPackStatus LzmaUtilImpl::UnPack(const base::FilePath& location,
         // Unmap the target file from the process's address space.
         mapped_file.reset();
         last_folder_index = -1;
-        // Flush to avoid an interesting bug in Windows 7 through Windows 10
-        // 1809; see
-        // https://randomascii.wordpress.com/2018/02/25/compiler-bug-linker-bug-windows-kernel-bug/
-        // for details.
-        if (base::win::GetVersion() < base::win::Version::WIN10_RS5)
-          target_file.Flush();
+        // Flush to avoid odd behavior, such as the bug in Windows 7 through
+        // Windows 10 1809 for PE files described in
+        // https://randomascii.wordpress.com/2018/02/25/compiler-bug-linker-bug-windows-kernel-bug/.
+        // We've also observed oddly empty files on other Windows versions, so
+        // this is unconditional.
+        target_file.Flush();
       }
     }