Add a "pub global run" command.

sdk/lib/_internal/pub/test/run/app_can_read_from_stdin_test.dart

Index: sdk/lib/_internal/pub/test/run/app_can_read_from_stdin_test.dart
diff --git a/sdk/lib/_internal/pub/test/run/app_can_read_from_stdin_test.dart b/sdk/lib/_internal/pub/test/run/app_can_read_from_stdin_test.dart
index 3dbb70312a8e489b2c12d125012ba79226a5d4f6..3a316047dddf990b7971e9be8130817f208096f9 100644
--- a/sdk/lib/_internal/pub/test/run/app_can_read_from_stdin_test.dart
+++ b/sdk/lib/_internal/pub/test/run/app_can_read_from_stdin_test.dart
@@ -4,12 +4,12 @@
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
-import 'utils.dart';
 
 const SCRIPT = """
 import 'dart:io';
 
 main() {
+  print("started");
   var line1 = stdin.readLineSync();
   print("between");
   var line2 = stdin.readLineSync();
@@ -30,6 +30,7 @@ main() {
 
     var pub = pubRun(args: ["script"]);
 
+    pub.stdout.expect("started");
     pub.writeLine("first");
     pub.stdout.expect("between");
     pub.writeLine("second");