Fix several bugs in closure conversion.

pkg/kernel/testcases/closures/blocks.dart

+// Copyright (c) 2017, 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.
+//
+// This test checks that we don't create duplicate local contexts in the same
+// function. It's modeled after the 'startIsolateMock' function which was broken
+// in the standard library.
+class X {}
+
+typedef dynamic fn(dynamic x);
+typedef dynamic fn2(dynamic x, dynamic y);
+
+void startIsolateMock(
+    dynamic parentPort,
+    dynamic entryPoint,
+    dynamic args,
+    dynamic message,
+    dynamic isSpawnUri,
+    dynamic controlPort,
+    List<dynamic> capabilities) {
+  if (controlPort != null) {
+    controlPort.handler = (dynamic _) {};
+  }
+  if (parentPort != null) {
+    dynamic readyMessage = new List<dynamic>(2);
+    readyMessage[0] = controlPort.sendPort;
+    readyMessage[1] = capabilities;
+    capabilities = null;
+    parentPort.send(readyMessage);
+  }
+  assert(capabilities == null);
+  dynamic port = "abc";
+  port.handler = (dynamic _) {
+    port.close();
+    if (isSpawnUri) {
+      if (entryPoint is fn2) {
+        entryPoint.call(args, message);
+      } else if (entryPoint is fn) {
+        entryPoint.call(args);
+      } else {
+        entryPoint.call();
+      }
+    } else {
+      entryPoint.call(message);
+    }
+  };
+  port.sendPort.send(null);
+}
+
+main() {
+  // No code here -- we just check that duplicate contexts aren't created above.
+}