Temporarily add debug logging for b/31357497

Note the check can't be a DCHECK because 103-string-append runs with the
non-debug build (libart.so).

Bug: 31357497
Bug: 12687968
Test: run-test 103-string-append on N9.
Change-Id: I30ebe9111fa6c42796dcafa182ae066214805173
1 file changed