dark_mode: Remove UnifiedSystemTrayView::CreateBackground.

Call sites of UnifiedSystemTrayView::CreateBackground have been removed
at crrev.com/c/2015577. The background of system tray now is controlled
inside TrayBubbleView by UnifiedSystemTrayView::GetBackgroundColor().

SwitchAccessBackButtonView doesn't inherit from TrayBubbleView, it
should not use the related logic. And its color is actually controlled
inside SwitchAccessBackButtonView::OnPaint.

Bug: 1107056
Change-Id: I13a8ac764fa6fbaa1dede9bdc7b3f6fedfe95b14
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2430323Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Min Chen <minch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810483}

ash/system/accessibility/switch_access_back_button_bubble_controller.cc

@@ -9,7 +9,6 @@
 #include "ash/system/accessibility/switch_access_back_button_view.h"
 #include "ash/system/tray/tray_background_view.h"
 #include "ash/system/tray/tray_constants.h"
-#include "ash/system/unified/unified_system_tray_view.h"
 #include "ui/accessibility/ax_enums.mojom.h"
 #include "ui/display/display.h"
 #include "ui/display/screen.h"
@@ -31,7 +30,6 @@ void SwitchAccessBackButtonBubbleController::ShowBackButton(
     bool for_menu) {
   if (!widget_) {
     back_button_view_ = new SwitchAccessBackButtonView(for_menu);
-    back_button_view_->SetBackground(UnifiedSystemTrayView::CreateBackground());
 
     TrayBubbleView::InitParams init_params;
     init_params.delegate = this;
@@ -43,11 +41,11 @@ void SwitchAccessBackButtonBubbleController::ShowBackButton(
     init_params.is_anchored_to_status_area = false;
     init_params.has_shadow = false;
     init_params.preferred_width = back_button_view_->size().width();
+    init_params.translucent = true;
 
     bubble_view_ = new TrayBubbleView(init_params);
     bubble_view_->SetArrow(views::BubbleBorder::BOTTOM_RIGHT);
     bubble_view_->AddChildView(back_button_view_);
-    bubble_view_->set_color(SK_ColorTRANSPARENT);
     bubble_view_->SetPaintToLayer();
     bubble_view_->layer()->SetFillsBoundsOpaquely(false);
 

ash/system/unified/unified_system_tray_view.cc

@@ -183,13 +183,6 @@ SkColor UnifiedSystemTrayView::GetFocusRingColor() {
   return ShelfConfig::Get()->shelf_focus_border_color();
 }
 
-// static
-std::unique_ptr<views::Background> UnifiedSystemTrayView::CreateBackground() {
-  return views::CreateBackgroundFromPainter(
-      views::Painter::CreateSolidRoundRectPainter(GetBackgroundColor(),
-                                                  kUnifiedTrayCornerRadius));
-}
-
 UnifiedSystemTrayView::UnifiedSystemTrayView(
     UnifiedSystemTrayController* controller,
     bool initially_expanded)

ash/system/unified/unified_system_tray_view.h

@@ -71,9 +71,6 @@ class ASH_EXPORT UnifiedSystemTrayView : public views::View,
   // Get focus ring color for system tray elements.
   static SkColor GetFocusRingColor();
 
-  // Create background of UnifiedSystemTray with rounded corners.
-  static std::unique_ptr<views::Background> CreateBackground();
-
   UnifiedSystemTrayView(UnifiedSystemTrayController* controller,
                         bool initially_expanded);
   ~UnifiedSystemTrayView() override;