Pass patched_sdk path down to fasta as an Uri.

tools/patch_sdk.dart

 #!/usr/bin/env dart
 // Copyright (c) 2015, 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.
 
 /// Command line tool to merge the SDK libraries and our patch files.
 /// This is currently designed as an offline tool, but we could automate it.
 
 import 'dart:io';
 import 'dart:async';
@@ skipping 188 matching lines @@
   // TODO(kustermann): We suppress compiler hints/warnings/errors temporarily
   // because everyone building the `runtime` target will get these now.
   // We should remove the suppression again once the underlying issues have
   // been fixed (either in fasta or the dart files in the patched_sdk).
   final capturedLines = <String>[];
   try {
     await runZoned(() async {
       await compile_platform.main(<String>[
         '--packages',
         new Uri.file(packagesFile).toString(),
-        outDir,
+        new Uri.directory(outDir).toString(),
         path.join(outDir, 'platform.dill')
       ]);
     }, zoneSpecification: new ZoneSpecification(print: (_, _2, _3, line) {
       capturedLines.add(line);
     }));
   } catch (_) {
     for (final line in capturedLines) {
       print(line);
     }
     rethrow;
@@ skipping 334 matching lines @@
     if (diff != 0) return diff;
     return end - other.end;
   }
 }
 
 List<SdkLibrary> _getSdkLibraries(String contents) {
   var libraryBuilder = new SdkLibrariesReader_LibraryBuilder(true);
   parseCompilationUnit(contents).accept(libraryBuilder);
   return libraryBuilder.librariesMap.sdkLibraries;
 }