Reload native extensions when starting from a snapshot.

samples/sample_extension/test/sample_extension_test_helper.dart

+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// 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.
+//
+// Dart test program for testing native extensions.
+
+import 'dart:async';
+import 'dart:io';
+import 'dart:isolate';
+
+import "package:expect/expect.dart";
+import "package:path/path.dart";
+
+Future copyFileToDirectory(String file, String directory) {
+  String src = file;
+  String dst = directory;
+  switch (Platform.operatingSystem) {
+    case 'linux':
+    case 'macos':
+      return Process.run('cp', [src, dst]);
+    case 'windows':
+      return Process.run('cmd.exe', ['/C', 'copy $src $dst']);
+    default:
+      Expect.fail('Unknown operating system ${Platform.operatingSystem}');
+  }
+}
+
+String getNativeLibraryPath(String buildDirectory) {
+  switch (Platform.operatingSystem) {
+    case 'linux':
+      return join(buildDirectory, 'lib.target', 'libsample_extension.so');
+    case 'macos':
+      return join(buildDirectory, 'libsample_extension.dylib');
+    case 'windows':
+      return join(buildDirectory, 'sample_extension.dll');
+    default:
+      Expect.fail('Unknown operating system ${Platform.operatingSystem}');
+  }
+}
+
+Future run(String program, List arguments) async {
+  print("+ $program ${arguments.join(' ')}");
+  ProcessResult result = await Process.run(program, arguments);
+  if (result.exitCode != 0) {
+    print('Failing process stdout: ${result.stdout}');
+    print('Failing process stderr: ${result.stderr}');
+    print('End failing process stderr');
+    Expect.fail('Test failed with exit code ${result.exitCode}');
+  }
+}
+
+Future testNativeExtensions(String snapshotKind) async {
+  String buildDirectory = dirname(Platform.executable);
+  Directory tempDirectory =
+      Directory.systemTemp.createTempSync('sample_extension_');
+  try {
+    String testDirectory = tempDirectory.path;
+    String sourceDirectory = Platform.script.resolve('..').toFilePath();
+
+    // Copy sample_extension shared library, sample_extension dart files and
+    // sample_extension tests to the temporary test directory.
+    await copyFileToDirectory(getNativeLibraryPath(buildDirectory),
+                              testDirectory);
+    for (var file in ['sample_synchronous_extension.dart',
+                      'sample_asynchronous_extension.dart',
+                      'test_sample_synchronous_extension.dart',
+                      'test_sample_asynchronous_extension.dart']) {
+      await copyFileToDirectory(join(sourceDirectory, file), testDirectory);
+    }
+
+    for (var test in ['test_sample_synchronous_extension.dart',
+                      'test_sample_asynchronous_extension.dart']) {
+      String script = join(testDirectory, test);
+      String snapshot;
+      if (snapshotKind == null) {
+        snapshot = script;
+      } else {
+        snapshot = join(testDirectory, "$test.snapshot");
+        await run(Platform.executable,
+                  ['--snapshot=$snapshot',
+                   '--snapshot-kind=$snapshotKind',
+                   script]);
+      }
+
+      await run(Platform.executable, [snapshot]);
+    }
+  } finally {
+    await tempDirectory.deleteSync(recursive: true);
+  }
+}