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The isolate was being passed around, even though only its current zone was used. Pass that zone directly instead, giving two benefits: 1. helps prepare for the upcoming Isolate/Thread split, where "new(isolate)" must go, and 2. saves a pointer indirection at the allocation sites. Review URL: https://codereview.chromium.org//855533002 git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@42935 260f80e4-7a28-3924-810f-c04153c831b5