Make binstubs run snapshots directly when possible.

sdk/lib/_internal/pub/test/global/binstubs/binstub_runs_global_run_if_no_snapshot_test.dart

Index: sdk/lib/_internal/pub/test/global/binstubs/binstub_runs_global_run_if_no_snapshot_test.dart
diff --git a/sdk/lib/_internal/pub/test/global/binstubs/path_package_test.dart b/sdk/lib/_internal/pub/test/global/binstubs/binstub_runs_global_run_if_no_snapshot_test.dart
similarity index 64%
copy from sdk/lib/_internal/pub/test/global/binstubs/path_package_test.dart
copy to sdk/lib/_internal/pub/test/global/binstubs/binstub_runs_global_run_if_no_snapshot_test.dart
index a837f73a9b95c1421860d8273db493073bfc1771..da72ec3fb0741c86dc69ab4c6785f5185396667e 100644
--- a/sdk/lib/_internal/pub/test/global/binstubs/path_package_test.dart
+++ b/sdk/lib/_internal/pub/test/global/binstubs/binstub_runs_global_run_if_no_snapshot_test.dart
@@ -9,25 +9,26 @@ import '../../test_pub.dart';
 
 main() {
   initConfig();
-  integration("creates binstubs when activating a path package", () {
+  integration("the binstubs runs pub global run if there is no snapshot", () {
     d.dir("foo", [
       d.pubspec({
         "name": "foo",
         "executables": {
-          "foo": null
+          "foo-script": "script"
         }
       }),
       d.dir("bin", [
-        d.file("foo.dart", "main() => print('ok');")
+        d.file("script.dart", "main() => print('ok');")
       ])
     ]).create();
 
+    // Path packages are mutable, so no snapshot is created.
     schedulePub(args: ["global", "activate", "--source", "path", "../foo"],
-        output: contains("Installed executable foo."));
+        output: contains("Installed executable foo-script."));
 
     d.dir(cachePath, [
       d.dir("bin", [
-        d.matcherFile("foo", contains("pub global run foo:foo"))
+        d.matcherFile("foo-script", contains("pub global run foo:script"))
       ])
     ]).validate();
   });