Aura overlay scrollbars adjust color for dark backgrounds

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 6587ec1060157f7d69f0ee2227e92754c2046ace..51f81da8115be2f9d563aaa6551d67adaac3bb30 100644
--- a/ui/native_theme/native_theme_aura.cc
+++ b/ui/native_theme/native_theme_aura.cc
@@ -20,6 +20,7 @@
 #include "ui/gfx/path.h"
 #include "ui/gfx/skia_util.h"
 #include "ui/native_theme/common_theme.h"
+#include "ui/native_theme/material_design_constants.h"
 #include "ui/native_theme/native_theme_switches.h"
 
 namespace ui {
@@ -32,11 +33,11 @@ SkAlpha ThumbAlphaForState(NativeTheme::State state) {
     case NativeTheme::kDisabled:
       return 0x00;
     case NativeTheme::kHovered:
-      return overlay ? 0xB2 : 0x4D;
+      return overlay ? kMDScrollbarAlphaHovered : 0x4D;
     case NativeTheme::kNormal:
-      return overlay ? 0x8C : 0x33;
+      return overlay ? kMDScrollbarAlphaNormal : 0x33;
     case NativeTheme::kPressed:
-      return overlay ? 0xB2 : 0x80;
+      return overlay ? kMDScrollbarAlphaPressed : 0x80;
     case NativeTheme::kNumStates:
       break;
   }
@@ -51,10 +52,11 @@ SkAlpha ThumbStrokeAlphaForState(NativeTheme::State state) {
     case NativeTheme::kDisabled:
       return 0x00;
     case NativeTheme::kHovered:
+      return kMDScrollbarAlphaHovered;
     case NativeTheme::kPressed:
-      return 0x33;
+      return kMDScrollbarAlphaPressed;
     case NativeTheme::kNormal:
-      return 0x26;
+      return kMDScrollbarAlphaNormal;
     case NativeTheme::kNumStates:
       break;
   }
@@ -84,6 +86,11 @@ NativeThemeAura::NativeThemeAura() {
   set_scrollbar_button_length(0);
 #endif
 
+  if (IsOverlayScrollbarEnabled()) {
+    scrollbar_width_ =
+        kMDScrollbarThumbWidthPressed + kMDScrollbarStrokeWidth * 2;
+  }
+
   // Images and alphas declarations assume the following order.
   static_assert(kDisabled == 0, "states unexpectedly changed");
   static_assert(kHovered == 1, "states unexpectedly changed");
@@ -181,12 +188,14 @@ void NativeThemeAura::PaintScrollbarTrack(
 void NativeThemeAura::PaintScrollbarThumb(SkCanvas* canvas,
                                           Part part,
                                           State state,
-                                          const gfx::Rect& rect) const {
+                                          const gfx::Rect& rect,
+                                          ScrollbarOverlayStyle style) const {
   // Do not paint if state is disabled.
   if (state == kDisabled)
     return;
 
-  PaintScrollbarThumbStateTransition(canvas, part, state, state, 1.0, rect);
+  PaintScrollbarThumbStateTransition(canvas, part, state, state, 1.0, rect,
+                                     style);
 }
 
 void NativeThemeAura::PaintScrollbarThumbStateTransition(
@@ -195,21 +204,35 @@ void NativeThemeAura::PaintScrollbarThumbStateTransition(
     State start_state,
     State end_state,
     double progress,
-    const gfx::Rect& rect) const {
+    const gfx::Rect& rect,
+    ScrollbarOverlayStyle style) const {
   gfx::Rect thumb_rect(rect);
+  SkColor thumb_color;
   if (IsOverlayScrollbarEnabled()) {
     // In overlay mode, draw a stroke (border).
-    const int kStrokeWidth = 1;
+    const int kStrokeWidth = kMDScrollbarStrokeWidth;
     SkAlpha stroke_alpha = gfx::Tween::IntValueBetween(
         progress, ThumbStrokeAlphaForState(start_state),
         ThumbStrokeAlphaForState(end_state));
     SkPaint paint;
-    paint.setColor(SkColorSetA(SK_ColorWHITE, stroke_alpha));
+    paint.setColor(SkColorSetA(kMDScrollbarStrokeColor, stroke_alpha));
     paint.setStyle(SkPaint::kStroke_Style);
     paint.setStrokeWidth(kStrokeWidth);
+
+    // When stroking in skia, there's some surprising behavior so we need to
+    // inset the right and bottom edges first. See the discussion here:
+    // https://groups.google.com/forum/#!topic/skia-discuss/HGZcc3Z7w1Q
+    thumb_rect.Inset(0, 0, kStrokeWidth, kStrokeWidth);
     canvas->drawIRect(gfx::RectToSkIRect(thumb_rect), paint);
 
-    thumb_rect.Inset(kStrokeWidth, kStrokeWidth, kStrokeWidth, kStrokeWidth);
+    // Inset the top and left edges for filling in the stroke below.
+    thumb_rect.Inset(kStrokeWidth, kStrokeWidth, 0, 0);
+
+    // thumb_color = kMDScrollbarThumbColor;
+    if (style == ScrollbarOverlayStyleLight)
+      thumb_color = SK_ColorWHITE;
+    else
+      thumb_color = SK_ColorBLACK;
   } else {
     // If there are no scrollbuttons then provide some padding so that the thumb
     // doesn't touch the top of the track.
@@ -220,12 +243,14 @@ void NativeThemeAura::PaintScrollbarThumbStateTransition(
       thumb_rect.Inset(kThumbPadding, extra_padding);
     else
       thumb_rect.Inset(extra_padding, kThumbPadding);
+
+    thumb_color = SK_ColorBLACK;
   }
 
   SkPaint paint;
   SkAlpha alpha = gfx::Tween::IntValueBetween(
       progress, ThumbAlphaForState(start_state), ThumbAlphaForState(end_state));
-  paint.setColor(SkColorSetA(SK_ColorBLACK, alpha));
+  paint.setColor(SkColorSetA(thumb_color, alpha));
   canvas->drawIRect(gfx::RectToSkIRect(thumb_rect), paint);
 }