Avoid boxing loop variables that are only mutated in initializer or update

Avoid boxing loop variables that are only mutated in initializer or update

For example:

for (int i=0; i<10; i++) {
  getFoo(i).then((x) {
    x.doBar(i);
  });
}


BUG=
R=floitsch@google.com, karlklose@google.com

Committed: https://code.google.com/p/dart/source/detail?r=42809

[asgerf, 2015-01-13 13:16:21]

asgerf@google.com changed reviewers:
+ floitsch@google.com

[karlklose, 2015-01-13 13:22:47]

karlklose@google.com changed reviewers:
+ karlklose@google.com

[karlklose, 2015-01-13 13:22:47]

LGTM.

https://codereview.chromium.org/802813004/diff/1/tests/compiler/dart2js/forlo...
File tests/compiler/dart2js/forloop_box_test.dart (right):

https://codereview.chromium.org/802813004/diff/1/tests/compiler/dart2js/forlo...
tests/compiler/dart2js/forloop_box_test.dart:32:
Expect.isTrue(generated.contains('main_closure(i)'), 'for-loop variable was
boxed');
Break these strings to the next line.

[floitsch, 2015-01-13 14:05:57]

LGTM.

[asgerf, 2015-01-13 14:11:18]

Committed patchset #3 (id:40001) manually as 42809 (presubmit successful).