Implement most of String API.

dart/frog/file_system_vm.dart

Index: dart/frog/file_system_vm.dart
diff --git a/dart/frog/file_system_vm.dart b/dart/frog/file_system_vm.dart
index 7b2944e4af90d626d87e446c6106e293bb75b766..1d906fc4db982ef14934675aaed8dee6736a8286 100644
--- a/dart/frog/file_system_vm.dart
+++ b/dart/frog/file_system_vm.dart
@@ -5,6 +5,7 @@
 #library('file_system_vm');
 #import('dart:io');
 #import('file_system.dart');
+#import('dart:utf8');
 
 /** File system implementation using the vm api's. */
 class VMFileSystem implements FileSystem {
@@ -21,7 +22,7 @@ class VMFileSystem implements FileSystem {
     var buffer = new List<int>(length);
     var bytes = file.readListSync(buffer, 0, length);
     file.closeSync();
-    return new String.fromCharCodes(buffer);
+    return new String.fromCharCodes(Utf8Decoder.decodeUtf8(buffer));
   }
 
   bool fileExists(String filename) {