Improve the heuristics for "pub get" is needed.

lib/src/executable.dart

Index: lib/src/executable.dart
diff --git a/lib/src/executable.dart b/lib/src/executable.dart
index 65b276ee4cdbf5b5c430aa4d527d54fd687ca7a9..bd21b4d8301e0d90739eb64b9598455fb9387ac7 100644
--- a/lib/src/executable.dart
+++ b/lib/src/executable.dart
@@ -82,6 +82,10 @@ Future<int> runExecutable(Entrypoint entrypoint, String package,
       // default mode for them to run. We can't run them in a different mode
       // using the snapshot.
       mode == BarbackMode.RELEASE) {
+    // Since we don't access the package graph, this doesn't happen
+    // automatically.
+    entrypoint.assertUpToDate();
+
     return _runCachedExecutable(entrypoint, localSnapshotPath, args,
         checked: checked);
   }