Remove one source of non determinism in MethodInliner.

The results of multiple calls to DeadCodeElimination on different nodes depend on
the ordering.

Change-Id: I31882b7cd7a0965643e15c3859042efc24cb0c6a
Review-Link: https://gwt-review.googlesource.com/#/c/2490/

Review by: skybrian@google.com