Summary:
Ref T13249. Ref T11738. See PHI985. Currently, we have a crude heuristic for guessing what line in a source file provides the best context.
We get it wrong in a lot of cases, sometimes selecting very silly lines like "{". Although we can't always pick the same line a human would pick, we //can// pile on heuristics until this is less frequently completely wrong and perhaps eventually get it to work fairly well most of the time.
Pull the logic for this into a separate standalone class and make it testable to prepare for adding heuristics.
Test Plan: Ran unit tests, browsed various files in the web UI and saw as-good-or-better context selection.
Reviewers: amckinley
Reviewed By: amckinley
Maniphest Tasks: T13249, T11738
Differential Revision: https://secure.phabricator.com/D20171
