Make binstubs run snapshots directly when possible.

sdk/lib/_internal/pub_generated/test/global/binstubs/binstub_runs_executable_test.dart

Index: sdk/lib/_internal/pub_generated/test/global/binstubs/binstub_runs_executable_test.dart
diff --git a/sdk/lib/_internal/pub_generated/test/global/binstubs/binstub_runs_executable_test.dart b/sdk/lib/_internal/pub_generated/test/global/binstubs/binstub_runs_executable_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..1c7b9f87d1498b433993492ad7051ff81ce6512f
--- /dev/null
+++ b/sdk/lib/_internal/pub_generated/test/global/binstubs/binstub_runs_executable_test.dart
@@ -0,0 +1,42 @@
+import 'package:path/path.dart' as p;
+import 'package:scheduled_test/scheduled_process.dart';
+import '../../descriptor.dart' as d;
+import '../../test_pub.dart';
+main() {
+  initConfig();
+  integration("the generated binstub runs a snapshotted executable", () {
+    servePackages((builder) {
+      builder.serve("foo", "1.0.0", pubspec: {
+        "executables": {
+          "foo-script": "script"
+        }
+      },
+          contents: [
+              d.dir("bin", [d.file("script.dart", "main(args) => print('ok \$args');")])]);
+    });
+    schedulePub(args: ["global", "activate", "foo"]);
+    var process = new ScheduledProcess.start(
+        p.join(sandboxDir, cachePath, "bin/foo-script"),
+        ["arg1", "arg2"]);
+    process.stdout.expect("ok [arg1, arg2]");
+    process.shouldExit();
+  });
+  integration("the generated binstub runs a non-snapshotted executable", () {
+    d.dir("foo", [d.pubspec({
+        "name": "foo",
+        "executables": {
+          "foo-script": "script"
+        }
+      }),
+          d.dir(
+              "bin",
+              [d.file("script.dart", "main(args) => print('ok \$args');")])]).create();
+    schedulePub(args: ["global", "activate", "-spath", "../foo"]);
+    var process = new ScheduledProcess.start(
+        p.join(sandboxDir, cachePath, "bin/foo-script"),
+        ["arg1", "arg2"],
+        environment: getPubTestEnvironment());
+    process.stdout.expect("ok [arg1, arg2]");
+    process.shouldExit();
+  });
+}