Remove saving/restoring of the context at function entry.

tests/language/vm/closure_memory_retention_test.dart

+// Copyright (c) 2014, 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.
+// VMOptions=--old_gen_heap_size=50
+
+// Test that non-capturing closures don't retain unnecessary memory.
+
+import "package:expect/expect.dart";
+
+foo() {
+  return () { };
+}
+
+bar(a, b) {
+  f() => [a, b];

[hausner, 2014/10/30 17:07:27]

Would be nice to add a comment that explains what is happening here (or more
precisely what should NOT happen). 

Also, I suggest adding a comment explaining that a negative test outcome is that
the program runs out of heap memory.

[Florian Schneider, 2014/10/30 17:21:58]

Done.

+  return foo();
+}
+
+main() {
+  var closure = null;
+  for (var i = 0; i < 100; i++) {
+    closure = bar(closure, new List(1024 * 1024));
+  }
+  Expect.isTrue(closure is Function);
+}