Update alpha values when painting overlay scrollbars.

ui/native_theme/native_theme_aura.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/native_theme/native_theme_aura.h"
 
 #include <limits>
 #include <utility>
 
 #include "base/logging.h"
@@ skipping 182 matching lines @@
     return;
 
   TRACE_EVENT0("blink", "NativeThemeAura::PaintScrollbarThumb");
 
   SkAlpha thumb_alpha = SK_AlphaTRANSPARENT;
   gfx::Rect thumb_rect(rect);
   SkColor thumb_color;
 
   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.
     constexpr SkColor kOverlayScrollbarThumbColor[] = {SK_ColorBLACK,
                                                        SK_ColorWHITE};
     constexpr SkColor kOverlayScrollbarStrokeColor[] = {SK_ColorWHITE,
                                                         SK_ColorBLACK};
 
     thumb_color = kOverlayScrollbarThumbColor[theme];
 
@@ skipping 132 matching lines @@
 
 gfx::Rect NativeThemeAura::GetNinePatchAperture(Part part) const {
   DCHECK(SupportsNinePatch(part));
 
   return gfx::Rect(
       kOverlayScrollbarBorderPatchWidth, kOverlayScrollbarBorderPatchWidth,
       kOverlayScrollbarCenterPatchSize, kOverlayScrollbarCenterPatchSize);
 }
 
 }  // namespace ui