Don't do folder existence checks when parsing pub list results.

pkg/analyzer/lib/file_system/physical_file_system.dart

Index: pkg/analyzer/lib/file_system/physical_file_system.dart
diff --git a/pkg/analyzer/lib/file_system/physical_file_system.dart b/pkg/analyzer/lib/file_system/physical_file_system.dart
index 398e451d63e224e6d1dc6b1aefe501e6e1202a90..80997098310d70b0669f3f591baf23087489ea35 100644
--- a/pkg/analyzer/lib/file_system/physical_file_system.dart
+++ b/pkg/analyzer/lib/file_system/physical_file_system.dart
@@ -130,6 +130,13 @@ class _PhysicalFolder extends _PhysicalResource implements Folder {
   }
 
   @override
+  _PhysicalFolder getChildAssumingFolder(String relPath) {
+    String canonicalPath = canonicalizePath(relPath);
+    io.Directory directory = new io.Directory(canonicalPath);
+    return new _PhysicalFolder(directory);
+  }
+
+  @override
   List<Resource> getChildren() {
     List<Resource> children = <Resource>[];
     io.Directory directory = _entry as io.Directory;