Revert "Enable NativeWinOcclusion by default."

This reverts commit e2f0841e.

Reason for revert: <causes issues with Citrix and other remote desktops>

Original change's description:
> Enable NativeWinOcclusion by default.
> 
> Bug: 813093
> Change-Id: I17a6e74172bc994723a0c23fa3e8dabfc30a4f45
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1815546
> Reviewed-by: François Doray <fdoray@chromium.org>
> Reviewed-by: Scott Violet <sky@chromium.org>
> Commit-Queue: David Bienvenu <davidbienvenu@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#699119}

TBR=sky@chromium.org,fdoray@chromium.org,davidbienvenu@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 813093
Change-Id: I163b75d39ce4249cb77251a8de0a2c5eaa332d2c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1917679Reviewed-by: David Bienvenu <davidbienvenu@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: David Bienvenu <davidbienvenu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715407}

ui/base/ui_base_features.cc

@@ -13,7 +13,7 @@ namespace features {
 #if defined(OS_WIN)
 // If enabled, calculate native window occlusion - Windows-only.
 const base::Feature kCalculateNativeWinOcclusion{
-    "CalculateNativeWinOcclusion", base::FEATURE_ENABLED_BY_DEFAULT};
+    "CalculateNativeWinOcclusion", base::FEATURE_DISABLED_BY_DEFAULT};
 #endif  // OW_WIN
 
 #if defined(OS_CHROMEOS)