Fix some scrollbar track and border painting issues (#90311)

packages/flutter/lib/src/widgets/scrollbar.dart

@@ -428,37 +428,46 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
 
     final double x, y;
     final Size thumbSize, trackSize;
-    final Offset trackOffset;
+    final Offset trackOffset, borderStart, borderEnd;
 
     _debugAssertIsValidOrientation(resolvedOrientation);
+
     switch(resolvedOrientation) {
       case ScrollbarOrientation.left:
         thumbSize = Size(thickness, thumbExtent);
         trackSize = Size(thickness + 2 * crossAxisMargin, _trackExtent);
         x = crossAxisMargin + padding.left;
         y = _thumbOffset;
-        trackOffset = Offset(x - crossAxisMargin, 0.0);
+        trackOffset = Offset(x - crossAxisMargin, mainAxisMargin);
+        borderStart = trackOffset + Offset(trackSize.width, 0.0);
+        borderEnd = Offset(trackOffset.dx + trackSize.width, trackOffset.dy + _trackExtent);
         break;
       case ScrollbarOrientation.right:
         thumbSize = Size(thickness, thumbExtent);
         trackSize = Size(thickness + 2 * crossAxisMargin, _trackExtent);
         x = size.width - thickness - crossAxisMargin - padding.right;
         y = _thumbOffset;
-        trackOffset = Offset(x - crossAxisMargin, 0.0);
+        trackOffset = Offset(x - crossAxisMargin, mainAxisMargin);
+        borderStart = trackOffset;
+        borderEnd = Offset(trackOffset.dx, trackOffset.dy + _trackExtent);
         break;
       case ScrollbarOrientation.top:
         thumbSize = Size(thumbExtent, thickness);
         trackSize = Size(_trackExtent, thickness + 2 * crossAxisMargin);
         x = _thumbOffset;
         y = crossAxisMargin + padding.top;
-        trackOffset = Offset(0.0, y - crossAxisMargin);
+        trackOffset = Offset(mainAxisMargin, y - crossAxisMargin);
+        borderStart = trackOffset + Offset(0.0, trackSize.height);
+        borderEnd = Offset(trackOffset.dx + _trackExtent, trackOffset.dy + trackSize.height);
         break;
       case ScrollbarOrientation.bottom:
         thumbSize = Size(thumbExtent, thickness);
         trackSize = Size(_trackExtent, thickness + 2 * crossAxisMargin);
         x = _thumbOffset;
         y = size.height - thickness - crossAxisMargin - padding.bottom;
-        trackOffset = Offset(0.0, y - crossAxisMargin);
+        trackOffset = Offset(mainAxisMargin, y - crossAxisMargin);
+        borderStart = trackOffset;
+        borderEnd = Offset(trackOffset.dx + _trackExtent, trackOffset.dy);
         break;
     }
 
@@ -472,15 +481,10 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
       // Track
       canvas.drawRect(_trackRect!, _paintTrack());
       // Track Border
-      canvas.drawLine(
-        trackOffset,
-        Offset(trackOffset.dx, trackOffset.dy + _trackExtent),
-        _paintTrack(isBorder: true),
-      );
+      canvas.drawLine(borderStart, borderEnd, _paintTrack(isBorder: true));
       if (radius != null) {
         // Rounded rect thumb
-        canvas.drawRRect(
-            RRect.fromRectAndRadius(_thumbRect!, radius!), _paintThumb);
+        canvas.drawRRect(RRect.fromRectAndRadius(_thumbRect!, radius!), _paintThumb);
         return;
       }
       if (shape == null) {

packages/flutter/test/cupertino/scrollbar_test.dart

@@ -1112,11 +1112,11 @@ void main() {
       find.byType(CupertinoScrollbar),
       paints
         ..rect(
-          rect: const Rect.fromLTRB(0.0, 0.0, 9.0, 594.0),
+          rect: const Rect.fromLTRB(0.0, 3.0, 9.0, 597.0),
         )
         ..line(
-          p1: Offset.zero,
-          p2: const Offset(0.0, 594.0),
+          p1: const Offset(9.0, 3.0),
+          p2: const Offset(9.0, 597.0),
           strokeWidth: 1.0,
         )
         ..rrect(

packages/flutter/test/material/scrollbar_paint_test.dart

@@ -67,8 +67,8 @@ void main() {
           color: const Color(0x00000000),
         )
         ..line(
-          p1: Offset.zero,
-          p2: const Offset(0.0, 600.0),
+          p1: const Offset(4.0, 0.0),
+          p2: const Offset(4.0, 600.0),
           strokeWidth: 1.0,
           color: const Color(0x00000000),
         )

packages/flutter/test/material/scrollbar_test.dart

@@ -1546,8 +1546,8 @@ void main() {
           color: Colors.transparent,
         )
         ..line(
-          p1: Offset.zero,
-          p2: const Offset(0.0, 600.0),
+          p1: const Offset(4.0, 0.0),
+          p2: const Offset(4.0, 600.0),
           strokeWidth: 1.0,
           color: Colors.transparent,
         )

packages/flutter/test/material/scrollbar_theme_test.dart

@@ -174,19 +174,19 @@ void main() {
     final TestGesture gesture = await tester.createGesture(kind: ui.PointerDeviceKind.mouse);
     await gesture.addPointer();
     addTearDown(gesture.removePointer);
-    await gesture.moveTo(const Offset(794.0, 5.0));
+    await gesture.moveTo(const Offset(794.0, 15.0));
     await tester.pumpAndSettle();
 
     expect(
       find.byType(Scrollbar),
       paints
         ..rect(
-          rect: const Rect.fromLTRB(770.0, 0.0, 800.0, 580.0),
+          rect: const Rect.fromLTRB(770.0, 10.0, 800.0, 590.0),
           color: const Color(0xff000000),
         )
         ..line(
-          p1: const Offset(770.0, 0.0),
-          p2: const Offset(770.0, 580.0),
+          p1: const Offset(770.0, 10.0),
+          p2: const Offset(770.0, 590.0),
           strokeWidth: 1.0,
           color: const Color(0xffffeb3b),
         )

packages/flutter/test/widgets/scrollbar_test.dart

@@ -1524,7 +1524,7 @@ void main() {
     expect(
       find.byType(RawScrollbar),
       paints
-        ..rect(rect: const Rect.fromLTRB(794.0, 0.0, 800.0, 580.0))
+        ..rect(rect: const Rect.fromLTRB(794.0, 10.0, 800.0, 590.0))
         ..rect(rect: const Rect.fromLTRB(794.0, 10.0, 800.0, 358.0))
     );
   });