Return an absolute URI for Platform.script.

tests/standalone/io/process_environment_test.dart

Index: tests/standalone/io/process_environment_test.dart
diff --git a/tests/standalone/io/process_environment_test.dart b/tests/standalone/io/process_environment_test.dart
index c36ef8c8ddc5038ca3158d7399cf0ec56dd61eae..4376aab20ad44b357e55759188ec0688584c4fdd 100644
--- a/tests/standalone/io/process_environment_test.dart
+++ b/tests/standalone/io/process_environment_test.dart
@@ -20,6 +20,14 @@ runEnvironmentProcess(Map environment, name, includeParent, callback) {
               environment: environment,
               includeParentEnvironment: includeParent)
       .then((result) {
+        if (result.exitCode != 0) {
+          print('print_env.dart subprocess failed '
+                'with exit code ${result.exitCode}');
+          print('stdout:');
+          print(result.stdout);
+          print('stderr:');
+          print(result.stderr);
+        }
         Expect.equals(0, result.exitCode);
         callback(result.stdout);
       });