Alpha for overlay scrollbars decreased when hovered.

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 4b6742f795fc1ee9fec0e0ce63f11da37d94c27e..41ae4c9c3173b6c3feeac5617ae571f3af997e02 100644
--- a/ui/native_theme/native_theme_aura.cc
+++ b/ui/native_theme/native_theme_aura.cc
@@ -35,6 +35,9 @@ constexpr int kOverlayScrollbarMinimumLength = 12;
 constexpr SkAlpha kOverlayScrollbarAlphaNormal = 0x4D;
 constexpr SkAlpha kOverlayScrollbarAlphaHovered = 0x80;
 constexpr SkAlpha kOverlayScrollbarAlphaPressed = 0x80;
+constexpr SkAlpha kOverlayStrokeAlphaNormal = 0x4D;

[Evan Stade, 2016/12/15 22:02:49]

nit: the naming on these constants is a little inconsistent. It would be more
symmetric if it were OverlayScrollbarFillAlpha vs OverlayScrollbarStrokeAlpha.
That said, I would be in favor of inlining all these since they're only used
once, and getting rid of the ones that don't differ between stroke and fill.

[bokan, 2016/12/15 22:05:30]

Agreed on naming. Personally, I like having named constants since it makes it
easy to see where the style values are coming from and where to change but a
middle ground might be to move them into the scope where they're used.

+constexpr SkAlpha kOverlayStrokeAlphaHovered = 0x58;
+constexpr SkAlpha kOverlayStrokeAlphaPressed = 0x80;
 
 // Indexed by ScrollbarOverlayColorTheme.
 constexpr SkColor kOverlayScrollbarThumbColor[] = {SK_ColorBLACK,
@@ -195,19 +198,24 @@ void NativeThemeAura::PaintScrollbarThumb(
   TRACE_EVENT0("blink", "NativeThemeAura::PaintScrollbarThumb");
 
   SkAlpha thumb_alpha = SK_AlphaTRANSPARENT;
+  SkAlpha stroke_alpha = SK_AlphaTRANSPARENT;
   const bool overlay = use_overlay_scrollbars_;
   switch (state) {
     case NativeTheme::kDisabled:
       thumb_alpha = SK_AlphaTRANSPARENT;
+      stroke_alpha = SK_AlphaTRANSPARENT;
       break;
     case NativeTheme::kHovered:
       thumb_alpha = overlay ? kOverlayScrollbarAlphaHovered : 0x4D;
+      stroke_alpha = overlay ? kOverlayStrokeAlphaHovered : 0x4D;
       break;
     case NativeTheme::kNormal:
       thumb_alpha = overlay ? kOverlayScrollbarAlphaNormal : 0x33;
+      stroke_alpha = overlay ? kOverlayStrokeAlphaNormal : 0x33;
       break;
     case NativeTheme::kPressed:
       thumb_alpha = overlay ? kOverlayScrollbarAlphaPressed : 0x80;
+      stroke_alpha = overlay ? kOverlayStrokeAlphaPressed : 0x80;

[Evan Stade, 2016/12/15 22:02:49]

stroke_alpha is unused when !overlay

       break;
     case NativeTheme::kNumStates:
       NOTREACHED();
@@ -223,7 +231,7 @@ void NativeThemeAura::PaintScrollbarThumb(
     constexpr int kStrokeWidth = kOverlayScrollbarStrokeWidth;
     SkPaint paint;
     paint.setColor(
-        SkColorSetA(kOverlayScrollbarStrokeColor[theme], thumb_alpha));
+        SkColorSetA(kOverlayScrollbarStrokeColor[theme], stroke_alpha));
     paint.setStyle(SkPaint::kStroke_Style);
     paint.setStrokeWidth(kStrokeWidth);