Revert "Adapt String interface for Utf16."

runtime/lib/string_base.dart

Index: runtime/lib/string_base.dart
diff --git a/runtime/lib/string_base.dart b/runtime/lib/string_base.dart
index 39f4518eb159c77dfe0456bb266d1d0fad211137..1f6d9fe7bfd28d5fc6cb0b00bd53f13943978722 100644
--- a/runtime/lib/string_base.dart
+++ b/runtime/lib/string_base.dart
@@ -38,11 +38,7 @@ class _StringBase {
 
   String operator [](int index) native "String_charAt";
 
-  int charCodeAt(int index) {
-    return codeUnitAt(index);
-  }
-
-  int codeUnitAt(int index) native "String_charCodeAt";
+  int charCodeAt(int index) native "String_charCodeAt";
 
   int get length native "String_getLength";
 
@@ -433,14 +429,6 @@ class _StringBase {
     return result;
   }
 
-  Iterable<int> get codeUnits {
-    throw new UnimplementedError("String.codeUnits");
-  }
-
-  Iterable<int> get runes {
-    throw new UnimplementedError("String.runes");
-  }
-
   String toUpperCase() native "String_toUpperCase";
 
   String toLowerCase() native "String_toLowerCase";