Remove cpuTimeAcc from DataSource#createSegmentMapFunction's signature

[kgyrtkirk]

This patch remove cpuTimeAcc from DataSource#createSegmentMapFunction signature.

the method being executed doesn't need to know internally that they are being measured; it also complicates code-flow a bit - as it tries to avoid double counting.

[clintropolis]

added design review label since this is modifying the signature of an extension point

[kgyrtkirk]

I don't think DataSource is api - its not marked with the annotations

I haven't seen any implementations of it outside the core modules (except one in msq)

git grep DataSource|fgrep -f <(echo extends;echo implements)|grep -v 'DataSourceMetadata'|grep -v /test/|less

in fact the current way things work; if someone would add a new datasource would have a pretty rough time running that on msq ; or having it work correctly in joins.

The issues I've seen can't be fixed without altering the Datasource api; unless I cheat with proxies/etc.

[clintropolis]

I don't think DataSource is api - its not marked with the annotations

I haven't seen any implementations of it outside the core modules (except one in msq)
in fact the current way things work; if someone would add a new datasource would have a pretty rough time running that on msq ; or having it work correctly in joins.

The issues I've seen can't be fixed without altering the Datasource api; unless I cheat with proxies/etc.

Yea, i did this out of an abundance of caution on changing stuff on core APIs, you're right that DataSource isn't directly marked, but Query is, and queries have a DataSource so any custom query engines would likely need to be rebuilt to account for the signature change.

That said, I think this change makes sense to make, so will approve after I finish reviewing, we just need to be sure to call it out in the dev oriented release notes.