In patch_sdk when passing --packages down to fasta turn it into 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:math' as math;
@@ skipping 177 matching lines @@
     }
 
     for (var file in ['loader.dart', 'server.dart', 'vmservice_io.dart']) {
       var libraryIn  = path.join(dartDir, 'runtime', 'bin', 'vmservice', file);
       var libraryOut = path.join(sdkOut, 'vmservice_io', file);
       _writeSync(libraryOut, new File(libraryIn).readAsStringSync());
     }
   }
 
   await compile_platform.main(<String>[
-    '--packages', packagesFile, sdkOut, path.join(sdkOut, 'platform.dill')
+    '--packages',
+    new Uri.file(packagesFile).toString(),
+    sdkOut,
+    path.join(sdkOut, 'platform.dill')
   ]);
 }
 
 /// Writes a file, creating the directory if needed.
 void _writeSync(String filePath, String contents) {
   var outDir = new Directory(path.dirname(filePath));
   if (!outDir.existsSync()) outDir.createSync(recursive: true);
 
   new File(filePath).writeAsStringSync(contents);
 }
@@ skipping 324 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;
 }