Remove deprecated string features.

tools/dom/src/KeyboardEventController.dart

Index: tools/dom/src/KeyboardEventController.dart
diff --git a/tools/dom/src/KeyboardEventController.dart b/tools/dom/src/KeyboardEventController.dart
index 73a7602f83b26cdb3e8bdcf09687cd9f40a85922..4235b754ce6dd5073dfeb34eae59a0639a5472d8 100644
--- a/tools/dom/src/KeyboardEventController.dart
+++ b/tools/dom/src/KeyboardEventController.dart
@@ -35,7 +35,7 @@ class KeyboardEventController {
   EventTarget _target;
 
   // The distance to shift from upper case alphabet Roman letters to lower case.
-  final int _ROMAN_ALPHABET_OFFSET = "a".charCodes[0] - "A".charCodes[0];
+  final int _ROMAN_ALPHABET_OFFSET = "a".codeUnits[0] - "A".codeUnits[0];
 
   StreamSubscription _keyUpSubscription, _keyDownSubscription,
       _keyPressSubscription;
@@ -170,8 +170,8 @@ class KeyboardEventController {
       if (prevEvent._shadowCharCode == event.charCode) {
         return prevEvent.keyCode;
       }
-      if ((event.shiftKey || _capsLockOn) && event.charCode >= "A".charCodes[0]
-          && event.charCode <= "Z".charCodes[0] && event.charCode +
+      if ((event.shiftKey || _capsLockOn) && event.charCode >= "A".codeUnits[0]
+          && event.charCode <= "Z".codeUnits[0] && event.charCode +
           _ROMAN_ALPHABET_OFFSET == prevEvent._shadowCharCode) {
         return prevEvent.keyCode;
       }