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

runtime/lib/isolate_patch.dart

Index: runtime/lib/isolate_patch.dart
diff --git a/runtime/lib/isolate_patch.dart b/runtime/lib/isolate_patch.dart
index 51b7ac0123147c1e9103d2875bf0efae471fcf42..daaaf9729f1444dffe5bd40ce83e7a2a53809c99 100644
--- a/runtime/lib/isolate_patch.dart
+++ b/runtime/lib/isolate_patch.dart
@@ -309,13 +309,15 @@ patch class Isolate {
   /* patch */ 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}) {
     RawReceivePort readyPort;
+    if (environment != null) throw new UnimplementedError("environment");
     try {
       // The VM will invoke [_startIsolate] and not `main`.
       // TODO: Handle [packages].