WebShare: no storage static_library on Windows

Avoids Step "compile confirm no-op" failing on builder
"win32-archive-rel" from
https://chromium-review.googlesource.com/c/chromium/src/+/2615664

Bug: 1144920,1164175
Change-Id: Ib8c8d3ac5869547d82cfd89740b1f057affccb09
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2615729Reviewed-by: Jiewei Qian  <qjw@chromium.org>
Commit-Queue: Eric Willigers <ericwilligers@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841394}

chrome/browser/webshare/BUILD.gn

@@ -4,8 +4,8 @@
 
 import("//build/config/chromeos/ui_mode.gni")
 
-static_library("storage") {
-  if (is_chromeos || is_mac) {
+if (is_chromeos || is_mac) {
+  static_library("storage") {
     sources = [
       "prepare_directory_task.cc",
       "prepare_directory_task.h",