Fixes for the 'pub' bot and 'analysis_server' on Windows.

pkg/analyzer/lib/file_system/memory_file_system.dart

Index: pkg/analyzer/lib/file_system/memory_file_system.dart
diff --git a/pkg/analyzer/lib/file_system/memory_file_system.dart b/pkg/analyzer/lib/file_system/memory_file_system.dart
index 39430d8dc4180f08eff9459a1f38ffbbac6fccbb..69e10442e0a8d803fcd36f5b0210f775b47509a0 100644
--- a/pkg/analyzer/lib/file_system/memory_file_system.dart
+++ b/pkg/analyzer/lib/file_system/memory_file_system.dart
@@ -186,7 +186,7 @@ class _MemoryFile extends _MemoryResource implements File {
   @override
   Source createSource([Uri uri]) {
     if (uri == null) {
-      uri = toUri(path);
+      uri = posix.toUri(path);
     }
     return new _MemoryFileSource(this, uri);
   }