Fix race in debug assertion.
Fix race in debug assertion.

Change order of initialization for the two-way pointers between Isolate and Thread.

This only affects the debug assertion in Isolate::mutator_thread().

R=iposva@google.com

Review URL: https://codereview.chromium.org//1138643006

git-svn-id: c93d8a2297af3b929165606efe145742a534bc71@45814 260f80e4-7a28-3924-810f-c04153c831b5

dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk