GN: Fix single-file compilations in VS2017 projects

Setting the "WindowsTargetPlatformVersion" XML element seems to
be necessary in VS2017. Single-file compilations do not work
without it. It does not cause any problems in older VS versions.

R=brettw@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2858273002
Cr-Original-Commit-Position: refs/heads/master@{#472272}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: d77555bcaf03f30f100c8ac72d598d14ef63153f
diff --git a/visual_studio_writer.cc b/visual_studio_writer.cc
index aa01d82..a498fb9 100644
--- a/visual_studio_writer.cc
+++ b/visual_studio_writer.cc
@@ -435,6 +435,8 @@
     globals->SubElement("RootNamespace")->Text(target->label().name());
     globals->SubElement("IgnoreWarnCompileDuplicatedFilename")->Text("true");
     globals->SubElement("PreferredToolArchitecture")->Text("x64");
+    globals->SubElement("WindowsTargetPlatformVersion")
+        ->Text(kWindowsKitsIncludeVersion);
   }
 
   project.SubElement(