[web] Fix conic to quad conversion assertion. (#18811)

* Fix subdivision assertion in Conic to Quad conversion

* Use const for upper bound

* remove unused import

Author: ferhatb

lib/web_ui/lib/src/engine/conic.dart

@@ -33,7 +33,7 @@ class Conic {
 
     // Split conic into quads, writes quad coordinates into [_pointList] and
     // returns number of quads.
-    assert(subdivideCount > 0);
+    assert(subdivideCount >= 0 && subdivideCount <= _maxSubdivisionCount);
     int quadCount = 1 << subdivideCount;
     bool skipSubdivide = false;
     pointList.add(ui.Offset(p0x, p0y));

lib/web_ui/test/path_test.dart

@@ -3,9 +3,9 @@
 // found in the LICENSE file.
 
 // @dart = 2.6
-import 'package:test/test.dart';
 import 'dart:js_util' as js_util;
 import 'dart:html' as html;
+import 'package:test/test.dart';
 import 'package:ui/ui.dart' hide window;
 import 'package:ui/src/engine.dart';
 
@@ -309,4 +309,10 @@ void main() {
     expect(path2.contains(Offset(100, 100)), isFalse);
     expect(path2.contains(Offset(50, 100)), isFalse);
   });
+
+  test('Should convert conic to quad when approximation error is small', () {
+    Conic conic = Conic(120.0, 20.0, 160.99470420829266, 20.0,
+        190.19301120261332, 34.38770865870253, 0.9252691032413082);
+    expect(conic.toQuads().length, 3);
+  });
 }