overview: Revert always animate blur on exit overview.

Suspected cl is hurting performance test in the bug. This was requested
by a couple people, we can see if this fixes it and then discuss with
ux a workaround.

Test: manual
Bug: 863304
Change-Id: I0dfdcc87cdfe99e80021cd8a94168bb976fbc02d
Reviewed-on: https://chromium-review.googlesource.com/1188438Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585880}

ash/wm/overview/window_selector_controller.cc

@@ -196,7 +196,7 @@ class WindowSelectorController::OverviewBlurController
     DCHECK(window_selector);
 
     for (aura::Window* root : Shell::Get()->GetAllRootWindows()) {
-      if (!should_blur || window_selector->ShouldAnimateWallpaper(root)) {
+      if (window_selector->ShouldAnimateWallpaper(root)) {
         root->AddObserver(this);
         roots_to_animate_.push_back(root);
       } else {