Previously when we put offsets into the SourcePositionTable, we added
the header size of the code object as well. When we pull the positions
out of the table (see ProfileGenerator::RecordTickSample) we already
account for the header size. This means the offsets in the table should
just be the offset of the PC within the actual code, not the offset
within the code object, which is what we currently store.

Currently this bug is probably not very noticeable, as it causes the
reported line numbers to be slightly too low, but still within the same
function. For a sampling profiler, we don't have any way to confirm
which lines were actually sampled, so we don't notice that the results
are wrong. The only way to see this bug is that there are some lines
within a function (towards the end of the function) that we will never
see ticks inside of, because the offset in the position table is not
reachable with valid PC offsets.

This CL removes the header size offset from values put into the source
position table stored by the profiler.

Bug: v8:7018
Change-Id: I00b17cec5f9c81d993d4e64c3c021052745a791e
Reviewed-on: https://chromium-review.googlesource.com/1016560Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52671}