CrOS Shelf: Slightly larger 'overshoot' margin to prevent tear-off

Bug: 996417
Change-Id: I63497b2b03110a68bc5f1b64feaeda8ab8792b80
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1811816Reviewed-by: Matthew Mourgos <mmourgos@chromium.org>
Commit-Queue: Manu Cornet <manucornet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697859}

ash/shelf/shelf_widget.cc

@@ -47,7 +47,7 @@ namespace {
 constexpr int kShelfBlurRadius = 30;
 // The maximum size of the opaque layer during an "overshoot" (drag away from
 // the screen edge).
-constexpr int kShelfMaxOvershootHeight = 32;
+constexpr int kShelfMaxOvershootHeight = 40;
 constexpr float kShelfBlurQuality = 0.33f;
 
 // Return the first or last focusable child of |root|.