Move away from using GetProminentColor for ScrollableUserListView

ProminentColors are eventually going away.  Resolve color using a
ColorId instead.

(cherry picked from commit 128b2d8)

Bug: b:291009599, b:291119801
Change-Id: I85241e4b01e8336399ba37752413b0d54a0e29b6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4682876
Reviewed-by: Denis Kuznetsov <antrim@chromium.org>
Commit-Queue: Sean Kau <skau@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#1171290}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4766139
Auto-Submit: Sean Kau <skau@chromium.org>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Commit-Queue: Maksim Ivanov <emaxx@chromium.org>
Cr-Commit-Position: refs/branch-heads/5845@{#1324}
Cr-Branched-From: 5a5dff6-refs/heads/main@{#1160321}

ash/login/ui/scrollable_users_list_view.cc

@@ -130,10 +130,9 @@ ScrollableUsersListView::GradientParams::BuildForStyle(LoginDisplayStyle style,
                                                        views::View* view) {
   switch (style) {
     case LoginDisplayStyle::kExtraSmall: {
-      SkColor dark_muted_color =
-          Shell::Get()->wallpaper_controller()->GetProminentColor(
-              color_utils::ColorProfile(color_utils::LumaRange::DARK,
-                                        color_utils::SaturationRange::MUTED));
+      SkColor dark_muted_color = view->GetColorProvider()->GetColor(
+          kColorAshLoginScrollableUserListBackground);
+
       SkColor tint_color = color_utils::GetResultingPaintColor(
           view->GetColorProvider()->GetColor(kColorAshShieldAndBase80),
           SkColorSetA(dark_muted_color, SK_AlphaOPAQUE));

ash/style/ash_color_id.h

@@ -132,7 +132,9 @@ namespace ash {
   /* Color for the background of the phantom window */ \
   E_CPONLY(kColorAshPhantomWindowBackgroundColor) \
   /* Color for the stroke on the window header view */ \
-  E_CPONLY(kColorAshWindowHeaderStrokeColor)
+  E_CPONLY(kColorAshWindowHeaderStrokeColor) \
+  /* Color for the 6+ scrollable list view on the login screen */ \
+  E_CPONLY(kColorAshLoginScrollableUserListBackground)
 
 #include "ui/color/color_id_macros.inc"
 

ash/style/ash_color_mixer.cc

@@ -693,6 +693,11 @@ void AddAshColorMixer(ui::ColorProvider* provider,
   mixer[kColorAshWindowHeaderStrokeColor] =
       ui::SetAlpha(cros_tokens::kCrosRefNeutral0, kAlpha8);
 
+  // Color for the scrollable user view on login.
+  mixer[kColorAshLoginScrollableUserListBackground] = {
+      use_dark_color ? cros_tokens::kCrosRefNeutral20
+                     : cros_tokens::kCrosRefNeutral80};
+
   mixer[ui::kColorToggleButtonThumbOn] = {cros_tokens::kCrosSysOnPrimary};
   mixer[ui::kColorToggleButtonThumbOff] = {cros_tokens::kCrosSysOnSecondary};
   mixer[ui::kColorToggleButtonThumbOnDisabled] =