Get binstubs working on Windows.

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

 import 'dart:io';
 import 'package:path/path.dart' as p;
 import 'package:scheduled_test/scheduled_process.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
+import 'utils.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"),
+        p.join(sandboxDir, cachePath, "bin", binStubName("foo-script")),
         ["arg1", "arg2"],
         environment: getEnvironment());
     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"),
+        p.join(sandboxDir, cachePath, "bin", binStubName("foo-script")),
         ["arg1", "arg2"],
         environment: getEnvironment());
     process.stdout.expect("ok [arg1, arg2]");
     process.shouldExit();
   });
 }
 getEnvironment() {
   var binDir = p.dirname(Platform.executable);
   var separator = Platform.operatingSystem == "windows" ? ";" : ":";
   var path = "${Platform.environment["PATH"]}$separator$binDir";
   var environment = getPubTestEnvironment();
   environment["PATH"] = path;
   return environment;
 }