Bug 987188 - Guard against a null pointer when dumping the layer tree. r=nical
Bug 903030 - Add tests for TextTrackCue validation code. r=cpearce
Bug 987297 - Improve memory usage of profiler by packing ProfileEntry structs together better. r=bgirard
Bug 989755: Fix up serialization of the grid-template shorthand. r=dholbert

* Refuse to serialize some combinations of values that the shorthand
  can not represent: 'grid-template-areas: (not none)' combined with
  'grid-template-rows: subgrid' or 'grid-template-columns: subgrid'.
  (The former used to cause an assertion failure.)
* Remove an extraneous trailing space that occured when a <track-list>
  was last. (ie. followed by an omitted <line-names>)
* Add tests for the result of this serialization.