Fix drawRRect failure when shader is specified (#16601)

lib/web_ui/dev/goldens_lock.yaml

 repository: https://github.com/flutter/goldens.git
-revision: 956d4e1862b108b31afd06cbf0a767cefc72f4c5
+revision: 1699ba6fd7093a0a610f82618fa30546e7974777

lib/web_ui/lib/src/engine/surface/recording_canvas.dart

@@ -228,7 +228,7 @@ class RecordingCanvas {
   }
 
   void drawRRect(ui.RRect rrect, SurfacePaint paint) {
-    if (!rrect.webOnlyUniformRadii) {
+    if (paint.shader != null || !rrect.webOnlyUniformRadii) {
       _hasArbitraryPaint = true;
     }
     _didDraw = true;

lib/web_ui/test/golden_tests/engine/linear_gradient_golden_test.dart

+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:html' as html;
+
+import 'package:ui/ui.dart' hide TextStyle;
+import 'package:ui/src/engine.dart';
+import 'package:test/test.dart';
+
+import 'package:web_engine_tester/golden_tester.dart';
+
+void main() async {
+  const double screenWidth = 600.0;
+  const double screenHeight = 800.0;
+  const Rect screenRect = Rect.fromLTWH(0, 0, screenWidth, screenHeight);
+
+  // Commit a recording canvas to a bitmap, and compare with the expected
+  Future<void> _checkScreenshot(RecordingCanvas rc, String fileName,
+      {Rect region = const Rect.fromLTWH(0, 0, 500, 500),
+        bool write = false}) async {
+    final EngineCanvas engineCanvas = BitmapCanvas(screenRect);
+    rc.apply(engineCanvas);
+
+    // Wrap in <flt-scene> so that our CSS selectors kick in.
+    final html.Element sceneElement = html.Element.tag('flt-scene');
+    try {
+      sceneElement.append(engineCanvas.rootElement);
+      html.document.body.append(sceneElement);
+      await matchGoldenFile('$fileName.png', region: region);
+    } finally {
+      // The page is reused across tests, so remove the element after taking the
+      // golden screenshot.
+      sceneElement.remove();
+    }
+  }
+
+  setUp(() async {
+    debugEmulateFlutterTesterEnvironment = true;
+    await webOnlyInitializePlatform();
+    webOnlyFontCollection.debugRegisterTestFonts();
+    await webOnlyFontCollection.ensureFontsLoaded();
+  });
+
+  test('Should draw linear gradient using rectangle.', () async {
+    final RecordingCanvas rc =
+      RecordingCanvas(const Rect.fromLTRB(0, 0, 500, 500));
+    Rect shaderRect = const Rect.fromLTRB(50, 50, 300, 300);
+    final Paint paint = Paint()..shader = Gradient.linear(
+        Offset(shaderRect.left, shaderRect.top),
+        Offset(shaderRect.right, shaderRect.bottom),
+        [Color(0xFFcfdfd2), Color(0xFF042a85)]);
+    rc.drawRect(shaderRect, paint);
+    expect(rc.hasArbitraryPaint, isTrue);
+    await _checkScreenshot(rc, 'linear_gradient_rect');
+  });
+
+  // Regression test for https://github.com/flutter/flutter/issues/50010
+  test('Should draw linear gradient using rounded rect.', () async {
+    final RecordingCanvas rc =
+    RecordingCanvas(const Rect.fromLTRB(0, 0, 500, 500));
+    Rect shaderRect = const Rect.fromLTRB(50, 50, 300, 300);
+    final Paint paint = Paint()..shader = Gradient.linear(
+        Offset(shaderRect.left, shaderRect.top),
+        Offset(shaderRect.right, shaderRect.bottom),
+        [Color(0xFFcfdfd2), Color(0xFF042a85)]);
+    rc.drawRRect(RRect.fromRectAndRadius(shaderRect, Radius.circular(16)), paint);
+    expect(rc.hasArbitraryPaint, isTrue);
+    await _checkScreenshot(rc, 'linear_gradient_rounded_rect');
+  });
+}