ART: Refactor IRT:Add

Do not abort on overflow. Return null and an error message. The
caller is responsible for handling this, e.g., by aborting. In a
future CL, this may be used for driving additional GCs.

Additional side effect is the removal of a frame from an abortion
stack trace.

Test: m
Test: m test-art-host
Change-Id: I80b1e0ee396fc69906d051f1b661d7dba222fc6f