Overlay scrollbars flush with window edge

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 168 matching lines @@
   cc::PaintFlags flags;
   flags.setColor(kTrackColor);
   canvas->drawIRect(gfx::RectToSkIRect(rect), flags);
 }
 
 void NativeThemeAura::PaintScrollbarThumb(
     cc::PaintCanvas* canvas,
     Part part,
     State state,
     const gfx::Rect& rect,
-    ScrollbarOverlayColorTheme theme) const {
+    const NativeTheme::ScrollbarThumbExtraParams& params) const {
   // Do not paint if state is disabled.
   if (state == kDisabled)
     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 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};
 
-    thumb_color = kOverlayScrollbarThumbColor[theme];
+    thumb_color = kOverlayScrollbarThumbColor[params.scrollbar_theme];
 
     SkAlpha stroke_alpha = SK_AlphaTRANSPARENT;
     switch (state) {
       case NativeTheme::kDisabled:
         thumb_alpha = SK_AlphaTRANSPARENT;
         stroke_alpha = SK_AlphaTRANSPARENT;
         break;
       case NativeTheme::kHovered:
         thumb_alpha = kOverlayScrollbarFillAlphaHovered;
         stroke_alpha = kOverlayScrollbarStrokeAlphaHovered;
         break;
       case NativeTheme::kNormal:
         thumb_alpha = kOverlayScrollbarFillAlphaNormal;
         stroke_alpha = kOverlayScrollbarStrokeAlphaNormal;
         break;
       case NativeTheme::kPressed:
         thumb_alpha = kOverlayScrollbarFillAlphaPressed;
         stroke_alpha = kOverlayScrollbarStrokeAlphaPressed;
         break;
       case NativeTheme::kNumStates:
         NOTREACHED();
         break;
     }
 
     // In overlay mode, draw a stroke (border).
     constexpr int kStrokeWidth = kOverlayScrollbarStrokeWidth;
     cc::PaintFlags flags;
-    flags.setColor(
-        SkColorSetA(kOverlayScrollbarStrokeColor[theme], stroke_alpha));
+    flags.setColor(SkColorSetA(
+        kOverlayScrollbarStrokeColor[params.scrollbar_theme], stroke_alpha));
     flags.setStyle(cc::PaintFlags::kStroke_Style);
     flags.setStrokeWidth(kStrokeWidth);
 
     gfx::RectF stroke_rect(thumb_rect);
     constexpr float kHalfStrokeWidth = kStrokeWidth / 2.f;
     stroke_rect.Inset(kHalfStrokeWidth, kHalfStrokeWidth);
     canvas->drawRect(gfx::RectFToSkRect(stroke_rect), flags);
 
     // Inset the all the edges edges so we fill-in the stroke below.
-    thumb_rect.Inset(kStrokeWidth, kStrokeWidth);
+    // The edge to which the scrollbar is attached shouldn't have a border.
+    if (part == NativeTheme::kScrollbarVerticalThumb) {

[Evan Stade, 2017/03/28 00:01:56]

nit: this can be clearer/less nested, e.g.

gfx::Insets insets(kStrokeWidth);
if (part == Horizontal)
  insets -= gfx::Insets(0,0,kStrokeWidth,0);
else if (isLeftVertical)
  insets -= gfx::Insets(0,kStrokeWidth,0,0);
else
  insets -= gfx::Insets(0,0,0,kStrokeWidth);
thumb_rect.Inset(insets);

+      if (params.isLeftVerticalScrollbar)
+        thumb_rect.Inset(0, kStrokeWidth, kStrokeWidth, kStrokeWidth);
+      else
+        thumb_rect.Inset(kStrokeWidth, kStrokeWidth, 0, kStrokeWidth);
+    } else {
+      thumb_rect.Inset(kStrokeWidth, kStrokeWidth, kStrokeWidth, 0);
+    }
   } else {
     switch (state) {
       case NativeTheme::kDisabled:
         thumb_alpha = SK_AlphaTRANSPARENT;
         break;
       case NativeTheme::kHovered:
         thumb_alpha = 0x4D;
         break;
       case NativeTheme::kNormal:
         thumb_alpha = 0x33;
@@ skipping 75 matching lines @@
 
 gfx::Rect NativeThemeAura::GetNinePatchAperture(Part part) const {
   DCHECK(SupportsNinePatch(part));
 
   return gfx::Rect(
       kOverlayScrollbarBorderPatchWidth, kOverlayScrollbarBorderPatchWidth,
       kOverlayScrollbarCenterPatchSize, kOverlayScrollbarCenterPatchSize);
 }
 
 }  // namespace ui