Omnibox UI Experiments: Fix narrow-dropdown appearance for Harmony

Small fix to adjust the Omnibox suggestions dropdown for the new
Harmony (kSecondaryUiMd enabled) BubbleBorder.

Bug: 783778
Change-Id: Id0b2a9e962aad098f46d53d1eedffad668639221
Reviewed-on: https://chromium-review.googlesource.com/831046Reviewed-by: Justin Donnelly <jdonnelly@chromium.org>
Commit-Queue: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524727}

chrome/browser/ui/views/omnibox/omnibox_popup_contents_view.cc

@@ -242,9 +242,7 @@ void OmniboxPopupContentsView::UpdatePopupAppearance() {
         background_color);
 
     // Outdent the popup to factor in the shadow size.
-    int border_thickness = border->GetBorderThickness();
-    new_target_bounds.Inset(-border_thickness, -border_thickness,
-                            -border_thickness, -border_thickness);
+    new_target_bounds.Inset(-border->GetInsets());
 
     SetBackground(base::MakeUnique<views::BubbleBackground>(border.get()));
     SetBorder(std::move(border));