It's anyway just the "same" AstNodeFactory (i.e., it's passed the same
AstValueFactory), so no need to have several of them for each
FunctionState.

R=verwaest@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2169823002
Cr-Commit-Position: refs/heads/master@{#37938}