ensure dart2js does not compile unsupported packages (#40368)

diff --git a/examples/platform_channel/pubspec.yaml b/examples/platform_channel/pubspec.yaml
index 9552e7c..c5287c7 100644
--- a/examples/platform_channel/pubspec.yaml
+++ b/examples/platform_channel/pubspec.yaml
@@ -27,7 +27,7 @@
   boolean_selector: 1.0.5 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   charcode: 1.1.2 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   convert: 2.1.1 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
-  crypto: 2.1.2 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
+  crypto: 2.1.3 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   csslib: 0.16.1 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   file: 5.0.10 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   front_end: 0.1.19 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
@@ -45,7 +45,7 @@
   matcher: 0.12.5 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   mime: 0.9.6+3 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   multi_server_socket: 1.0.2 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
-  node_preamble: 1.4.7 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
+  node_preamble: 1.4.8 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   package_config: 1.1.0 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   package_resolver: 1.0.10 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   path: 1.6.4 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
@@ -76,4 +76,4 @@
 flutter:
   uses-material-design: true
 
-# PUBSPEC CHECKSUM: 2bda
+# PUBSPEC CHECKSUM: a7dc