Make frog.py --leg work on Windows.

dart/frog/frog_leg.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #library('frog_leg');
 
 #import('dart:io');
 #import('dart:uri');
 
 #import('lang.dart', prefix: 'frog');
 #import('../lib/compiler/compiler.dart', prefix: 'compiler');
+#import('../lib/compiler/implementation/filenames.dart');
 
 String relativize(Uri base, Uri uri) {
   if (base.scheme == 'file' &&
       base.scheme == uri.scheme &&
       base.userInfo == uri.userInfo &&
       base.domain == uri.domain &&
       base.port == uri.port &&
       uri.query == "" && uri.fragment == "") {
     if (uri.path.startsWith(base.path)) {
       return uri.path.substring(base.path.length);
@@ skipping 16 matching lines @@
     return sb.toString();
   }
   return uri.toString();
 }
 
 bool compile(frog.World world) {
   final throwOnError = frog.options.throwOnErrors;
   final showWarnings = frog.options.showWarnings;
   final allowMockCompilation = frog.options.allowMockCompilation;
   Uri cwd = new Uri(scheme: 'file', path: getCurrentDirectory());
-  Uri uri = cwd.resolve(frog.options.dartScript);
-  String frogLibDir = frog.options.libDir;
+  Uri uri = cwd.resolve(nativeToUriPath(frog.options.dartScript));
+  String frogLibDir = nativeToUriPath(frog.options.libDir);
   if (!frogLibDir.endsWith("/")) frogLibDir = "$frogLibDir/";
   Uri frogLib = new Uri(scheme: 'file', path: frogLibDir);
   Uri libraryRoot = frogLib.resolve('../../');
   Map<String, frog.SourceFile> sourceFiles = <frog.SourceFile>{};
 
   Future<String> provider(Uri uri) {
     if (uri.scheme != 'file') {
       throw new IllegalArgumentException(uri);
     }
-    String source = world.files.readAll(uri.path);
+    String source = world.files.readAll(uriPathToNative(uri.path));
     world.dartBytesRead += source.length;
     sourceFiles[uri.toString()] =
       new frog.SourceFile(relativize(cwd, uri), source);
     Completer<String> completer = new Completer<String>();
     completer.complete(source);
     return completer.future;
   }
 
   void handler(Uri uri, int begin, int end, String message, bool fatal) {
     if (uri === null && !fatal) {
@@ skipping 27 matching lines @@
   final message;
   AbortLeg(this.message);
   toString() => 'Aborted due to --throw-on-error: $message';
 }
 
 String getCurrentDirectory() {
   String dir = new File(".").fullPathSync();
   if (dir.endsWith("/")) return dir;
   return "$dir/";
 }