Previously we would elide debug slots if the statement position it
belongs to has just already been written. The motivation is that since
we should only break once per statement, we can elide debug slots that
has the same statement position as the previous debug slot.

This is an unnecessary optimization, since the debugger has yet another
check against breaking twice at the same statement at runtime, in
Debug::Break.

This optimization can also be wrong, if there is control flow involved,
for example if we can jump to the elided debug slot without executing
the previous debug slot.

CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_chromium_rel_ng;tryserver.blink:linux_blink_rel
R=jgruber@chromium.org

Review-Url: https://codereview.chromium.org/2080173002
Cr-Commit-Position: refs/heads/master@{#37107}