Make pub's binstubs resilient to changes in snapshot format.

sdk/lib/_internal/pub/lib/src/entrypoint.dart

Index: sdk/lib/_internal/pub/lib/src/entrypoint.dart
diff --git a/sdk/lib/_internal/pub/lib/src/entrypoint.dart b/sdk/lib/_internal/pub/lib/src/entrypoint.dart
index 940efab97d5c5a9a67b311dca22ec2048c0a278f..5c2c8454d28963c6504371957d724f6a340add0b 100644
--- a/sdk/lib/_internal/pub/lib/src/entrypoint.dart
+++ b/sdk/lib/_internal/pub/lib/src/entrypoint.dart
@@ -348,6 +348,10 @@ class Entrypoint {
   /// contains dependencies that are not in the lockfile or that don't match
   /// what's in there.
   bool _isLockFileUpToDate(LockFile lockFile) {
+    /// If this is an entrypoint for an in-memory package, trust the in-memory
+    /// lockfile provided for it.
+    if (root.dir == null) return true;
+
     return root.immediateDependencies.every((package) {
       var locked = lockFile.packages[package.name];
       if (locked == null) return false;