[BUGFIX release] Add missing HistoryLocation code that was lost in manual merge from es6 => stable

@rjackson As discussed on IRC, currently the `stable` branch is failing tests 2965, 2966 on an *actual* browser but not Travis. Most likely cause Travis doesn't support `history` so a different code path is being taken since `HistoryLocation` is still lacking full test coverage.

This code is from https://github.com/emberjs/ember.js/commit/3e695d7bb276b821c018c29dde655f7394d51a74

but was accidentally lost here https://github.com/emberjs/ember.js/commit/07fafb8445664bc94fc68b70bb4d4cf668d1cbd9 when manually merged into stable due to es6 conflicts.