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..6f85aa2f44ba48177f6357bd5d3ddef5e17fbe04 100644
--- a/ui/native_theme/native_theme_aura.cc
+++ b/ui/native_theme/native_theme_aura.cc
@@ -32,15 +32,6 @@ namespace {
 // this painting code are defined in overlay_scrollbar_constants_aura.h.
 constexpr int kOverlayScrollbarStrokeWidth = 1;
 constexpr int kOverlayScrollbarMinimumLength = 12;
-constexpr SkAlpha kOverlayScrollbarAlphaNormal = 0x4D;
-constexpr SkAlpha kOverlayScrollbarAlphaHovered = 0x80;
-constexpr SkAlpha kOverlayScrollbarAlphaPressed = 0x80;
-
-// Indexed by ScrollbarOverlayColorTheme.
-constexpr SkColor kOverlayScrollbarThumbColor[] = {SK_ColorBLACK,
-                                                   SK_ColorWHITE};
-constexpr SkColor kOverlayScrollbarStrokeColor[] = {SK_ColorWHITE,
-                                                    SK_ColorBLACK};
 
 const SkColor kTrackColor = SkColorSetRGB(0xF1, 0xF1, 0xF1);
 
@@ -194,20 +185,39 @@ void NativeThemeAura::PaintScrollbarThumb(
 
   TRACE_EVENT0("blink", "NativeThemeAura::PaintScrollbarThumb");
 
+  // Constants used for painting overlay scrollbar thumb.
+  constexpr SkAlpha kOverlayScrollbarFillAlphaNormal = 0x4D;
+  constexpr SkAlpha kOverlayScrollbarFillAlphaHovered = 0x80;
+  constexpr SkAlpha kOverlayScrollbarFillAlphaPressed = 0x80;
+  constexpr SkAlpha kOverlayScrollbarStrokeAlphaNormal = 0x4D;
+  constexpr SkAlpha kOverlayScrollbarStrokeAlphaHovered = 0x58;
+  constexpr SkAlpha kOverlayScrollbarStrokeAlphaPressed = 0x80;
+
+  // Indexed by ScrollbarOverlayColorTheme.
+  constexpr SkColor kOverlayScrollbarThumbColor[] = {SK_ColorBLACK,
+                                                     SK_ColorWHITE};
+  constexpr SkColor kOverlayScrollbarStrokeColor[] = {SK_ColorWHITE,
+                                                      SK_ColorBLACK};
+
   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;
+      thumb_alpha = overlay ? kOverlayScrollbarFillAlphaHovered : 0x4D;
+      stroke_alpha = overlay ? kOverlayScrollbarStrokeAlphaHovered : 0x4D;
       break;
     case NativeTheme::kNormal:
-      thumb_alpha = overlay ? kOverlayScrollbarAlphaNormal : 0x33;
+      thumb_alpha = overlay ? kOverlayScrollbarFillAlphaNormal : 0x33;
+      stroke_alpha = overlay ? kOverlayScrollbarStrokeAlphaNormal : 0x33;
       break;
     case NativeTheme::kPressed:
-      thumb_alpha = overlay ? kOverlayScrollbarAlphaPressed : 0x80;
+      thumb_alpha = overlay ? kOverlayScrollbarFillAlphaPressed : 0x80;
+      stroke_alpha = overlay ? kOverlayScrollbarStrokeAlphaPressed : 0x80;

[Evan Stade, 2016/12/19 16:06:56]

this ternary still doesn't make sense to me because you never use it in the non
overlay case.

[sahel, 2016/12/19 17:57:26]

You are right, it's only used for overlay case. I wanted to do all the alpha
assignments in one part of code with one switch-case.
Done, moved it to overlay specific part of the function. 

       break;
     case NativeTheme::kNumStates:
       NOTREACHED();
@@ -223,7 +233,7 @@ 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);