Make use lists into doubly-linked lists.

Make use lists into doubly-linked lists.

At the cost of a word per use, we gain constant time removal from use
lists.

BUG=
Committed: https://code.google.com/p/dart/source/detail?r=17924

[Kevin Millikin (Google), 2013-01-31 12:44:54]

https://codereview.chromium.org/12079096/diff/1/runtime/vm/flow_graph_optimiz...
File runtime/vm/flow_graph_optimizer.cc (right):

https://codereview.chromium.org/12079096/diff/1/runtime/vm/flow_graph_optimiz...
runtime/vm/flow_graph_optimizer.cc:2242: use->RemoveFromInputUseList();
In another change, I will create a single operation for the pattern of
RemoveFromList/set_definition/AddToList.

[Vyacheslav Egorov (Google), 2013-01-31 13:42:19]

lgtm

https://codereview.chromium.org/12079096/diff/1/runtime/vm/intermediate_langu...
File runtime/vm/intermediate_language.cc (right):

https://codereview.chromium.org/12079096/diff/1/runtime/vm/intermediate_langu...
runtime/vm/intermediate_language.cc:668: current->AddToInputUseList();
I don't really understand why we adding them one by one instead of reattaching
the whole list to the other definition.

(the same below).

[Kevin Millikin (Google), 2013-01-31 13:46:47]

https://codereview.chromium.org/12079096/diff/1/runtime/vm/intermediate_langu...
File runtime/vm/intermediate_language.cc (right):

https://codereview.chromium.org/12079096/diff/1/runtime/vm/intermediate_langu...
runtime/vm/intermediate_language.cc:668: current->AddToInputUseList();
There's no good reason.  I'll change it.