cros: Disable overview cross fade blur.

Caused regression in attached bug. UX still wants this will try to
possibly re-enable this for M-80. But for M-79 we should disable it.

TBR=oshima@chromium.org

Test: none
Bug: 1016047
Change-Id: I41bee546750b712b575ff3ed70a6245009bcf0c7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1872767
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707984}

ash/public/cpp/ash_features.cc

@@ -56,7 +56,7 @@ const base::Feature kNotificationScrollBar{"NotificationScrollBar",
                                            base::FEATURE_DISABLED_BY_DEFAULT};
 
 const base::Feature kOverviewCrossFadeWallpaperBlur{
-    "OverviewCrossFadeWallpaperBlur", base::FEATURE_ENABLED_BY_DEFAULT};
+    "OverviewCrossFadeWallpaperBlur", base::FEATURE_DISABLED_BY_DEFAULT};
 
 const base::Feature kPipRoundedCorners{"PipRoundedCorners",
                                        base::FEATURE_DISABLED_BY_DEFAULT};