Background compilation work:

tests/language/vm/optimized_stacktrace_test.dart

 // Copyright (c) 2015, 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=--stacktrace-every=3 --optimization-counter-threshold=10 --enable-inlining-annotations
+// VMOptions=--stacktrace-every=3 --optimization-counter-threshold=10 --enable-inlining-annotations --no-background-compilation
 
 // Test generating stacktraces with inlining and deferred code.
 // Regression test for issue dartbug.com/22331
 
 class A {
   final N;
   final inc;
   var next;
   A(this.N, this.inc) {
     next = this;
@@ skipping 18 matching lines @@
   var value = 0x100000000 + o.inc;
   baz(0, 0, foo(o, value));
 }
 
 main() {
   var o = new A(10, 1);
   for (var i = 0; i < 100; i++) bar(o);
   bar(new A(100000, 1));
 }