Library root fix for win

pkg/dev_compiler/lib/src/compiler/code_generator.dart

Index: pkg/dev_compiler/lib/src/compiler/code_generator.dart
diff --git a/pkg/dev_compiler/lib/src/compiler/code_generator.dart b/pkg/dev_compiler/lib/src/compiler/code_generator.dart
index 7df66d29e2a33d9149355743fefa73b20995cab9..07ded75dc49e34019e05d192f1f943a4ff8fba22 100644
--- a/pkg/dev_compiler/lib/src/compiler/code_generator.dart
+++ b/pkg/dev_compiler/lib/src/compiler/code_generator.dart
@@ -6033,7 +6033,8 @@ String jsLibraryName(String libraryRoot, LibraryElement library) {
     // E.g., "foo/bar.dart" and "foo$47bar.dart" would collide.
     qualifiedPath = uri.pathSegments.skip(1).join(encodedSeparator);
   } else if (isWithin(libraryRoot, uri.toFilePath())) {
-    qualifiedPath = uri.path
+    qualifiedPath = uri
+        .toFilePath()
         .substring(libraryRoot.length)

[jakemac, 2017/05/24 18:25:17]

Should we change this to use `path.relative` as well, or save that for later?

         .replaceAll(separator, encodedSeparator);
   } else {