Add "environment" parameter to spawnUri for String.fromEnvironment support.

sdk/lib/_internal/js_runtime/lib/isolate_patch.dart

Index: sdk/lib/_internal/js_runtime/lib/isolate_patch.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/isolate_patch.dart b/sdk/lib/_internal/js_runtime/lib/isolate_patch.dart
index 70eda5b5e973708798fe729f2faf6b5eec296c82..f33a264597db0c357d9766d745694245ad878167 100644
--- a/sdk/lib/_internal/js_runtime/lib/isolate_patch.dart
+++ b/sdk/lib/_internal/js_runtime/lib/isolate_patch.dart
@@ -63,12 +63,14 @@ class Isolate {
   static Future<Isolate> spawnUri(
       Uri uri, List<String> args, var message,
       {bool paused: false,
+       SendPort onExit,
+       SendPort onError,
+       bool errorsAreFatal,
        bool checked,
+       Map<String, String> environment,
        Uri packageRoot,
-       Map<String, Uri> packages,
-       bool errorsAreFatal,
-       SendPort onExit,
-       SendPort onError}) {
+       Map<String, Uri> packages}) {
+    if (environment != null) throw new UnimplementedError("environment");
     if (packageRoot != null) throw new UnimplementedError("packageRoot");
     if (packages != null) throw new UnimplementedError("packages");
     bool forcePause = (errorsAreFatal != null) ||