Remove deprecated string features.

tests/standalone/io/string_decoder_test.dart

Index: tests/standalone/io/string_decoder_test.dart
diff --git a/tests/standalone/io/string_decoder_test.dart b/tests/standalone/io/string_decoder_test.dart
index 879cf8c0c57ec98b0355acc6b96e6b0939db36e9..2fcefd231cbbeea36d346323bdf164f2f176ef30 100644
--- a/tests/standalone/io/string_decoder_test.dart
+++ b/tests/standalone/io/string_decoder_test.dart
@@ -20,14 +20,14 @@ void test() {
     var decoded = sis.read();
     Expect.equals(7, decoded.length);
 
-    var replacementChar = '?'.charCodeAt(0);
-    Expect.equals(0xd800, decoded.charCodeAt(0));
-    Expect.equals(0xdc00, decoded.charCodeAt(1));
-    Expect.equals(0xdbff, decoded.charCodeAt(2));
-    Expect.equals(0xdfff, decoded.charCodeAt(3));
-    Expect.equals(replacementChar, decoded.charCodeAt(4));
-    Expect.equals(replacementChar, decoded.charCodeAt(5));
-    Expect.equals(replacementChar, decoded.charCodeAt(6));
+    var replacementChar = '?'.codeUnitAt(0);
+    Expect.equals(0xd800, decoded.codeUnitAt(0));
+    Expect.equals(0xdc00, decoded.codeUnitAt(1));
+    Expect.equals(0xdbff, decoded.codeUnitAt(2));
+    Expect.equals(0xdfff, decoded.codeUnitAt(3));
+    Expect.equals(replacementChar, decoded.codeUnitAt(4));
+    Expect.equals(replacementChar, decoded.codeUnitAt(5));
+    Expect.equals(replacementChar, decoded.codeUnitAt(6));
   };
 }