Don't use alloca.
Don't use alloca.

It leads to compability hell, and the amount of memory we need is bounded,
anyway. Added a few more assertions on the way.

Review URL: https://chromiumcodereview.appspot.com/10808029

git-svn-id: b158db1e4b4ab85d4c9e510fdef4b1e8c614b15b@12137 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh