Update desk thumbnail boarder color on new spec.

Bug: 988513
Change-Id: Icae273a3e57abbf09f154bc89ba8a37e7017fdec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1737347Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Min Chen <minch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684131}

ash/wm/desks/desk_mini_view.cc

@@ -23,9 +23,9 @@ constexpr int kLabelPreviewSpacing = 8;
 
 constexpr int kCloseButtonMargin = 4;
 
-constexpr SkColor kActiveColor = SkColorSetARGB(0xEE, 0xFF, 0xFF, 0xFF);
+constexpr SkColor kActiveColor = SkColorSetA(SK_ColorWHITE, 0xCC);  // 80%
 
-constexpr SkColor kInactiveColor = SkColorSetARGB(0x50, 0xFF, 0xFF, 0xFF);
+constexpr SkColor kInactiveColor = SkColorSetA(SK_ColorWHITE, 0x33);  // 20%
 
 constexpr SkColor kDraggedOverColor = SkColorSetARGB(0xFF, 0x5B, 0xBC, 0xFF);