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"
 #include "base/trace_event/trace_event.h"
 #include "build/build_config.h"
 #include "cc/paint/paint_canvas.h"
 #include "cc/paint/paint_flags.h"
 #include "ui/base/layout.h"
 #include "ui/base/material_design/material_design_controller.h"
 #include "ui/gfx/animation/tween.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/color_palette.h"
+#include "ui/gfx/geometry/insets.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/geometry/size.h"
 #include "ui/gfx/image/image_skia.h"
 #include "ui/gfx/path.h"
 #include "ui/gfx/skia_util.h"
 #include "ui/native_theme/common_theme.h"
 #include "ui/native_theme/native_theme_switches.h"
 #include "ui/native_theme/overlay_scrollbar_constants_aura.h"
 
 namespace ui {
@@ skipping 214 matching lines @@
         SkColorSetA(kOverlayScrollbarStrokeColor[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.
+    // For left vertical scrollbar, we will horizontally flip the canvas in
+    // ScrollbarThemeOverlay::paintThumb.
+    gfx::Insets insets(kStrokeWidth);
+    if (part == NativeTheme::kScrollbarHorizontalThumb)
+      insets -= gfx::Insets(0, 0, kStrokeWidth, 0);
+    else
+      insets -= gfx::Insets(0, 0, 0, kStrokeWidth);
+
+    thumb_rect.Inset(insets);
   } 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