Revert "Remove FX_Alloc() null checks now that it can't return NULL."

This reverts commit eb6527763171cdb4b0fbfea5a20d691f4d67b660.

Reason for revert: broke javascript tests.
TBR=thestig@chromium.org

Review URL: https://codereview.chromium.org/1145843005
48 files changed