Revert "Fix library name insert and access inconsistency on windows"

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 a642fe4da82618211f0ff3717842618acf9f03c7..9cbc9ec0944963f19f5db971f50c5027fa1cbfb1 100644
--- a/pkg/dev_compiler/lib/src/compiler/code_generator.dart
+++ b/pkg/dev_compiler/lib/src/compiler/code_generator.dart
@@ -31,7 +31,7 @@ import 'package:analyzer/src/summary/summarize_elements.dart'
 import 'package:analyzer/src/summary/summary_sdk.dart';
 import 'package:analyzer/src/task/strong/ast_properties.dart'
     show isDynamicInvoke, setIsDynamicInvoke, getImplicitAssignmentCast;
-import 'package:path/path.dart' show separator, isWithin, fromUri;
+import 'package:path/path.dart' show separator;
 
 import '../closure/closure_annotator.dart' show ClosureAnnotator;
 import '../js_ast/js_ast.dart' as JS;
@@ -5452,17 +5452,16 @@ String jsLibraryName(String libraryRoot, LibraryElement library) {
     return uri.path;
   }
   // TODO(vsm): This is not necessarily unique if '__' appears in a file name.
-  var customSeparator = '__';
+  var separator = '__';
   String qualifiedPath;
   if (uri.scheme == 'package') {
     // Strip the package name.
     // TODO(vsm): This is not unique if an escaped '/'appears in a filename.
     // E.g., "foo/bar.dart" and "foo$47bar.dart" would collide.
-    qualifiedPath = uri.pathSegments.skip(1).join(customSeparator);
-  } else if (isWithin(libraryRoot, uri.toFilePath())) {
-    qualifiedPath = fromUri(uri)
-        .substring(libraryRoot.length)
-        .replaceAll(separator, customSeparator);
+    qualifiedPath = uri.pathSegments.skip(1).join(separator);
+  } else if (uri.toFilePath().startsWith(libraryRoot)) {
+    qualifiedPath =
+        uri.path.substring(libraryRoot.length).replaceAll('/', separator);
   } else {
     // We don't have a unique name.
     throw 'Invalid library root. $libraryRoot does not contain ${uri