Fix flaky idle notification test.
Fix flaky idle notification test.

Idle notification handler might not free more memory if there was a global GC before or incremental marking is not activated (and it's not worth activating).

BUG=
TEST=cctest/test-api/IdleNotificationWithHint

Review URL: http://codereview.chromium.org/9173007

git-svn-id: b158db1e4b4ab85d4c9e510fdef4b1e8c614b15b@10401 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh