When updating source positions, we recompute reloc info. Under the
assumption that reloc info is appended to the code, we may or may not
need to allocate a new code object. That assumption is no longer valid
since 2010 (see r5020).

R=mstarzinger@chromium.org

Review-Url: https://codereview.chromium.org/2077363002
Cr-Commit-Position: refs/heads/master@{#37097}