dark_mode: Always set blur for system tray menu.

Themed system tray background was added at crrev.com/c/2006370 and
removed at crrev.com/c/2398988, since themed background is controlled
inside AshColorProvider after crrev.com/c/2242223.

- Remove the unnecessary logic inside GetBackgroundColor that was added
  to theme the system tray background color.
- Always add blur for system tray.

Then the background color of the system tray will always be
kTransparent80 with 30 blur sigma, based on the latest spec at
https://www.figma.com/file/rQFGy3iAMfNdDnydTGkvHr/Style-%7C-Semantic-color-system-surface-theming?node-id=372%3A0

Bug: 1130618
Change-Id: Ib38a30f6f287baa63a3f2544374224e526859e92
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2424646Reviewed-by: Tim Song <tengs@chromium.org>
Commit-Queue: Min Chen <minch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809607}

ash/system/tray/tray_bubble_view.cc

@@ -250,8 +250,7 @@ TrayBubbleView::TrayBubbleView(const InitParams& init_params)
     layer()->SetColor(UnifiedSystemTrayView::GetBackgroundColor());
     layer()->SetFillsBoundsOpaquely(false);
     layer()->SetIsFastRoundedCorner(true);
-    if (features::IsBackgroundBlurEnabled())
-      layer()->SetBackgroundBlur(kUnifiedMenuBackgroundBlur);
+    layer()->SetBackgroundBlur(kUnifiedMenuBackgroundBlur);
   } else {
     // Create a layer so that the layer for FocusRing stays in this view's
     // layer. Without it, the layer for FocusRing goes above the

ash/system/unified/unified_system_tray_view.cc

@@ -7,9 +7,8 @@
 #include <numeric>
 
 #include "ash/public/cpp/ash_features.h"
+#include "ash/public/cpp/shelf_config.h"
 #include "ash/session/session_controller_impl.h"
-#include "ash/shelf/shelf.h"
-#include "ash/shelf/shelf_widget.h"
 #include "ash/shell.h"
 #include "ash/style/ash_color_provider.h"
 #include "ash/system/media/unified_media_controls_container.h"
@@ -175,17 +174,8 @@ class UnifiedSystemTrayView::SystemTrayContainer : public views::View {
 
 // static
 SkColor UnifiedSystemTrayView::GetBackgroundColor() {
-  auto background_type = Shelf::ForWindow(Shell::GetPrimaryRootWindow())
-                             ->shelf_widget()
-                             ->GetBackgroundType();
-  AshColorProvider::BaseLayerType layer_type =
-      (background_type == ShelfBackgroundType::kMaximized ||
-       background_type == ShelfBackgroundType::kInApp) ||
-       !features::IsBackgroundBlurEnabled()
-          ? AshColorProvider::BaseLayerType::kTransparent90
-          : AshColorProvider::BaseLayerType::kTransparent80;
-
-  return AshColorProvider::Get()->GetBaseLayerColor(layer_type);
+  return AshColorProvider::Get()->GetBaseLayerColor(
+      AshColorProvider::BaseLayerType::kTransparent80);
 }
 
 // static