Reland #13918 (#14023)

* Revert "Reverting package changes until I can figure out how to fix Windows. (#14007)"

This reverts commit 6fda8ee821dd2e63e7949e57b10efde84bb0a3cc.

* Make prepare_package run on Windows

examples/flutter_gallery/pubspec.yaml

diff --git a/examples/flutter_gallery/pubspec.yaml b/examples/flutter_gallery/pubspec.yaml
index 201d6cc..24e5121 100644
--- a/examples/flutter_gallery/pubspec.yaml
+++ b/examples/flutter_gallery/pubspec.yaml
@@ -25,7 +25,7 @@
 
   args: 0.13.7 # TRANSITIVE DEPENDENCY
   async: 1.13.3 # TRANSITIVE DEPENDENCY
-  barback: 0.15.2+13 # TRANSITIVE DEPENDENCY
+  barback: 0.15.2+14 # TRANSITIVE DEPENDENCY
   boolean_selector: 1.0.2 # TRANSITIVE DEPENDENCY
   charcode: 1.1.1 # TRANSITIVE DEPENDENCY
   cli_util: 0.1.2+1 # TRANSITIVE DEPENDENCY
@@ -34,7 +34,7 @@
   csslib: 0.14.1 # TRANSITIVE DEPENDENCY
   file: 2.3.5 # TRANSITIVE DEPENDENCY
   glob: 1.1.5 # TRANSITIVE DEPENDENCY
-  html: 0.13.2+1 # TRANSITIVE DEPENDENCY
+  html: 0.13.2+2 # TRANSITIVE DEPENDENCY
   http: 0.11.3+14 # TRANSITIVE DEPENDENCY
   http_multi_server: 2.0.4 # TRANSITIVE DEPENDENCY
   http_parser: 3.1.1 # TRANSITIVE DEPENDENCY