Update alpha values when painting overlay scrollbars.

ui/native_theme/native_theme_aura.cc

Index: ui/native_theme/native_theme_aura.cc
diff --git a/ui/native_theme/native_theme_aura.cc b/ui/native_theme/native_theme_aura.cc
index b6c070242b5a2be459a84369062d8b9608b3c5d3..5c2a462e90f1b83947ca481a9020801aa78cc118 100644
--- a/ui/native_theme/native_theme_aura.cc
+++ b/ui/native_theme/native_theme_aura.cc
@@ -200,11 +200,11 @@ void NativeThemeAura::PaintScrollbarThumb(
 
   if (use_overlay_scrollbars_) {
     // Constants used for painting overlay scrollbar thumb.
-    constexpr SkAlpha kOverlayScrollbarFillAlphaNormal = 0x4D;
-    constexpr SkAlpha kOverlayScrollbarFillAlphaHovered = 0x80;
-    constexpr SkAlpha kOverlayScrollbarFillAlphaPressed = 0x80;
+    constexpr SkAlpha kOverlayScrollbarFillAlphaNormal = 0x80;
+    constexpr SkAlpha kOverlayScrollbarFillAlphaHovered = 0xB3;
+    constexpr SkAlpha kOverlayScrollbarFillAlphaPressed = 0xB3;
     constexpr SkAlpha kOverlayScrollbarStrokeAlphaNormal = 0x4D;
-    constexpr SkAlpha kOverlayScrollbarStrokeAlphaHovered = 0x58;
+    constexpr SkAlpha kOverlayScrollbarStrokeAlphaHovered = 0x80;
     constexpr SkAlpha kOverlayScrollbarStrokeAlphaPressed = 0x80;
 
     // Indexed by ScrollbarOverlayColorTheme.