Emit dex_pc as line number when debug info is unavailable for ANR traces

This commit makes ANR stack traces behave like Java stack traces when
we fail to map debug info to a line number. That is, we null out the
source_file and use the dex_pc as the line number.

Test: art/test.py -b --host
Change-Id: Ia1cceba439ba6912393415f5bc54199dcc0c3d23
1 file changed