Upgrade ScrollableUsersListView GradientParams on wallpaper change

Bug: 839610
Change-Id: I4a4ee5e8c80a57a32f8368fe3716803c82148183
Reviewed-on: https://chromium-review.googlesource.com/1086068Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Commit-Queue: Quan Nguyen <qnnguyen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#564957}

ash/login/ui/scrollable_users_list_view.cc

@@ -119,7 +119,7 @@ ScrollableUsersListView::ScrollableUsersListView(
     const std::vector<mojom::LoginUserInfoPtr>& users,
     const ActionWithUser& on_tap_user,
     LoginDisplayStyle display_style)
-    : views::ScrollView() {
+    : views::ScrollView(), observer_(this) {
   layout_params_ = GetLayoutParams(display_style);
   gradient_params_ = GetGradientParams(display_style);
 
@@ -154,6 +154,8 @@ ScrollableUsersListView::ScrollableUsersListView(
   hover_notifier_ = std::make_unique<HoverNotifier>(
       this, base::BindRepeating(&ScrollableUsersListView::OnHover,
                                 base::Unretained(this)));
+
+  observer_.Add(Shell::Get()->wallpaper_controller());
 }
 
 ScrollableUsersListView::~ScrollableUsersListView() = default;
@@ -216,6 +218,13 @@ void ScrollableUsersListView::OnPaintBackground(gfx::Canvas* canvas) {
   canvas->DrawRect(GetLocalBounds(), flags);
 }
 
+// When the active user is updated, the wallpaper changes. The gradient color
+// should be updated in response to the new primary wallpaper color.
+void ScrollableUsersListView::OnWallpaperColorsChanged() {
+  gradient_params_ = GetGradientParams(layout_params_.display_style);
+  SchedulePaint();
+}
+
 void ScrollableUsersListView::OnHover(bool has_hover) {
   scroll_bar_->SetThumbVisible(has_hover);
 }

ash/login/ui/scrollable_users_list_view.h

@@ -11,6 +11,9 @@
 #include "ash/login/ui/login_display_style.h"
 #include "ash/login/ui/login_user_view.h"
 #include "ash/public/interfaces/login_user_info.mojom.h"
+#include "ash/wallpaper/wallpaper_controller.h"
+#include "ash/wallpaper/wallpaper_controller_observer.h"
+#include "base/scoped_observer.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/views/controls/scroll_view.h"
 
@@ -27,7 +30,8 @@ class ScrollBar;
 // Scrollable list of the users. Stores the list of login user views. Can be
 // styled with GradientParams that define gradient tinting at the top and at the
 // bottom. Can be styled with LayoutParams that define spacing and sizing.
-class ASH_EXPORT ScrollableUsersListView : public views::ScrollView {
+class ASH_EXPORT ScrollableUsersListView : public views::ScrollView,
+                                           public WallpaperControllerObserver {
  public:
   // TestApi is used for tests to get internal implementation details.
   class ASH_EXPORT TestApi {
@@ -67,6 +71,9 @@ class ASH_EXPORT ScrollableUsersListView : public views::ScrollView {
   void Layout() override;
   void OnPaintBackground(gfx::Canvas* canvas) override;
 
+  // ash::WallpaperControllerObserver:
+  void OnWallpaperColorsChanged() override;
+
  private:
   struct GradientParams {
     // Start color for drawing linear gradient.
@@ -108,6 +115,8 @@ class ASH_EXPORT ScrollableUsersListView : public views::ScrollView {
   GradientParams gradient_params_;
   LayoutParams layout_params_;
 
+  ScopedObserver<WallpaperController, WallpaperControllerObserver> observer_;
+
   DISALLOW_COPY_AND_ASSIGN(ScrollableUsersListView);
 };