Clean up file implementation.

runtime/bin/directory_impl.dart

Index: runtime/bin/directory_impl.dart
diff --git a/runtime/bin/directory_impl.dart b/runtime/bin/directory_impl.dart
index 4df863048f9a5231c9e3187206c7c0511bba2296..23510f9004e02a7337f08f26d26fa1125c129a24 100644
--- a/runtime/bin/directory_impl.dart
+++ b/runtime/bin/directory_impl.dart
@@ -176,17 +176,17 @@ class _Directory implements Directory {
   String get path { return _path; }
 
   bool _isErrorResponse(response) {
-    return response is List && response[0] != _FileUtils.SUCCESS_RESPONSE;
+    return response is List && response[0] != _SUCCESS_RESPONSE;
   }
 
   Exception _exceptionFromResponse(response, String message) {
     assert(_isErrorResponse(response));
-    switch (response[_FileUtils.ERROR_RESPONSE_ERROR_TYPE]) {
-      case _FileUtils.ILLEGAL_ARGUMENT_RESPONSE:
+    switch (response[_ERROR_RESPONSE_ERROR_TYPE]) {
+      case _ILLEGAL_ARGUMENT_RESPONSE:
         return new ArgumentError();
-      case _FileUtils.OSERROR_RESPONSE:
-        var err = new OSError(response[_FileUtils.OSERROR_RESPONSE_MESSAGE],
-                              response[_FileUtils.OSERROR_RESPONSE_ERROR_CODE]);
+      case _OSERROR_RESPONSE:
+        var err = new OSError(response[_OSERROR_RESPONSE_MESSAGE],
+                              response[_OSERROR_RESPONSE_ERROR_CODE]);
         return new DirectoryIOException(message, _path, err);
       default:
         return new Exception("Unknown error");
@@ -238,14 +238,14 @@ class _DirectoryLister implements DirectoryLister {
           break;
         case LIST_ERROR:
           var errorType =
-              message[RESPONSE_ERROR][_FileUtils.ERROR_RESPONSE_ERROR_TYPE];
-          if (errorType == _FileUtils.ILLEGAL_ARGUMENT_RESPONSE) {
+              message[RESPONSE_ERROR][_ERROR_RESPONSE_ERROR_TYPE];
+          if (errorType == _ILLEGAL_ARGUMENT_RESPONSE) {
             _reportError(new ArgumentError());
-          } else if (errorType == _FileUtils.OSERROR_RESPONSE) {
+          } else if (errorType == _OSERROR_RESPONSE) {
             var responseError = message[RESPONSE_ERROR];
             var err = new OSError(
-                responseError[_FileUtils.OSERROR_RESPONSE_MESSAGE],
-                responseError[_FileUtils.OSERROR_RESPONSE_ERROR_CODE]);
+                responseError[_OSERROR_RESPONSE_MESSAGE],
+                responseError[_OSERROR_RESPONSE_ERROR_CODE]);
             var errorPath = message[RESPONSE_PATH];
             if (errorPath == null) errorPath = path;
             _reportError(new DirectoryIOException("Directory listing failed",