Create binstubs for executables when activating a package.

sdk/lib/_internal/pub_generated/lib/src/validator/executable.dart

Index: sdk/lib/_internal/pub_generated/lib/src/validator/executable.dart
diff --git a/sdk/lib/_internal/pub_generated/lib/src/validator/executable.dart b/sdk/lib/_internal/pub_generated/lib/src/validator/executable.dart
new file mode 100644
index 0000000000000000000000000000000000000000..f7a9d3aeca0670bb7e6de16395e1bf7be958bd22
--- /dev/null
+++ b/sdk/lib/_internal/pub_generated/lib/src/validator/executable.dart
@@ -0,0 +1,32 @@
+library pub.validator.compiled_dartdoc;
+import 'dart:async';
+import 'package:path/path.dart' as p;
+import '../entrypoint.dart';
+import '../io.dart';
+import '../utils.dart';
+import '../validator.dart';
+class ExecutableValidator extends Validator {
+  ExecutableValidator(Entrypoint entrypoint) : super(entrypoint);
+  Future validate() {
+    final completer0 = new Completer();
+    scheduleMicrotask(() {
+      try {
+        var binFiles = entrypoint.root.listFiles(
+            beneath: "bin",
+            recursive: false).map(
+                ((path) => p.relative(path, from: entrypoint.root.dir))).toList();
+        entrypoint.root.pubspec.executables.forEach(((executable, script) {
+          if (!binFiles.contains("bin/$script.dart")) {
+            warnings.add(
+                'Your pubspec.yaml lists an executable "$executable" that '
+                    'points to a script "bin/$script.dart" that does not exist.');
+          }
+        }));
+        completer0.complete(null);
+      } catch (e0) {
+        completer0.completeError(e0);
+      }
+    });
+    return completer0.future;
+  }
+}