Import of dart:ui to trigger Flutter compilation (#500)

diff --git a/lib/src/flutter_web.dart b/lib/src/flutter_web.dart
index 1a94a50..5a6c6bb 100644
--- a/lib/src/flutter_web.dart
+++ b/lib/src/flutter_web.dart
@@ -78,6 +78,7 @@
 
   static final Set<String> _flutterWebImportPrefixes = <String>{
     'package:flutter',
+    'dart:ui',
   };
 
   bool usesFlutterWeb(Set<String> imports) {
diff --git a/test/flutter_web_test.dart b/test/flutter_web_test.dart
index 0ac644d..9349dc2 100644
--- a/test/flutter_web_test.dart
+++ b/test/flutter_web_test.dart
@@ -33,6 +33,7 @@
     test('usesFlutterWeb', () {
       expect(flutterWebManager.usesFlutterWeb({''}), isFalse);
       expect(flutterWebManager.usesFlutterWeb({'dart:html'}), isFalse);
+      expect(flutterWebManager.usesFlutterWeb({'dart:ui'}), isTrue);
       expect(flutterWebManager.usesFlutterWeb({'package:flutter_web'}), isTrue);
       expect(
           flutterWebManager.usesFlutterWeb({'package:flutter_web/'}), isTrue);
@@ -40,6 +41,7 @@
 
     test('getUnsupportedImport', () {
       expect(flutterWebManager.getUnsupportedImport({'dart:html'}), isNull);
+      expect(flutterWebManager.getUnsupportedImport({'dart:ui'}), isNull);
       expect(flutterWebManager.getUnsupportedImport({'package:flutter_web/'}),
           isNull);
       expect(flutterWebManager.getUnsupportedImport({'package:path'}),