fix failing test

Author: LongCatIsLooong

lib/web_ui/test/html/text/canvas_paragraph_test.dart

@@ -776,7 +776,19 @@ Future<void> testMain() async {
     expect(paragraph.longestLine, 50.0);
   });
 
-  test('$CanvasParagraph.width should be a whole integer', () {
+  test('$CanvasParagraph.width should be a whole integer when shouldDisableRoundingHack is false', () {
+    if (ui.ParagraphBuilder.shouldDisableRoundingHack) {
+      // Try applying the rounding hack if it's disabled. This may not work if
+      // the 'SKPARAGRAPH_REMOVE_ROUNDING_HACK' dart environment declaration
+      // is set to 'false'.
+      ui.ParagraphBuilder.setDisableRoundingHack(false);
+      addTearDown(() => ui.ParagraphBuilder.setDisableRoundingHack(true));
+    }
+    // The paragraph width is only rounded to a whole integer if
+    // shouldDisableRoundingHack is false.
+    if (ui.ParagraphBuilder.shouldDisableRoundingHack) {
+      return;
+    }
     final ui.Paragraph paragraph = plain(ahemStyle, 'abc');
     paragraph.layout(const ui.ParagraphConstraints(width: 30.8));