Ensure dart and pub are on PATH when spawning binstub processes in test.

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

Index: sdk/lib/_internal/pub/test/global/binstubs/binstub_runs_executable_test.dart
diff --git a/sdk/lib/_internal/pub/test/global/binstubs/binstub_runs_executable_test.dart b/sdk/lib/_internal/pub/test/global/binstubs/binstub_runs_executable_test.dart
index 9abed5ae3f052a22e6925c8a2504ae6e7866b4b6..cc3fbdb9b76168d013a5680ca6176482b1529a76 100644
--- a/sdk/lib/_internal/pub/test/global/binstubs/binstub_runs_executable_test.dart
+++ b/sdk/lib/_internal/pub/test/global/binstubs/binstub_runs_executable_test.dart
@@ -2,8 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+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';
@@ -26,7 +29,8 @@ main() {
     schedulePub(args: ["global", "activate", "foo"]);
 
     var process = new ScheduledProcess.start(
-        p.join(sandboxDir, cachePath, "bin/foo-script"), ["arg1", "arg2"]);
+        p.join(sandboxDir, cachePath, "bin/foo-script"), ["arg1", "arg2"],
+        environment: getEnvironment());
 
     process.stdout.expect("ok [arg1, arg2]");
     process.shouldExit();
@@ -49,9 +53,22 @@ main() {
 
     var process = new ScheduledProcess.start(
         p.join(sandboxDir, cachePath, "bin/foo-script"), ["arg1", "arg2"],
-        environment: getPubTestEnvironment());
+        environment: getEnvironment());
 
     process.stdout.expect("ok [arg1, arg2]");
     process.shouldExit();
   });
 }
+
+/// The buildbots do not have the Dart SDK (containing "dart" and "pub") on
+/// their PATH, so we need to spawn the binstub process with a PATH that
+/// explicitly includes it.
+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;
+}