Adjust the blur quality to reduce flicker

Bug: 901433
Test: manual. See bug for repro step
Change-Id: Idd25bc0b0b0519141660b11cb7db5e67bc04122c
Reviewed-on: https://chromium-review.googlesource.com/c/1319855Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605769}

ash/app_list/views/app_list_view.cc

@@ -97,7 +97,7 @@ constexpr int kAppListBackgroundRadius = 28;
 constexpr int kAppListHomeLaucherGesturesThreshold = 32;
 
 // Quality of the shield background blur.
-constexpr float kAppListBlurQuality = 0.25f;
+constexpr float kAppListBlurQuality = 0.33f;
 
 // Set animation durations to 0 for testing.
 static bool short_animations_for_testing;