Add @extends annotations to generated externs
Do not extend goog.* types
Walk up the inheritance chain to an exportable constructor
Add base classes to info.json and generated externs

This ensures that the inheritance chain is intact, even if the base
class is not exportable.
Improve ol.Collection documentation
Merge pull request #2644 from ahocevar/extends-externs

Add @extends annotations to generated externs
Add @api to ol.Sphere
Merge pull request #2652 from fredj/collection-doc

Improve ol.Collection documentation
Add @classdesc to ol.Sphere
Make tissot example use ol.Sphere
Remove @api annotation from ol.sphere.WGS84
Merge pull request #2641 from elemoine/sphere

Add @api to ol.Sphere
New domain in the build header
Merge pull request #2660 from elemoine/domain

New domain in the build header
Add olx.layer.ImageOptions typedef
Set ol.layer.Image#getSource return type to ol.source.Image
Remove unnecessary type cast
Set ol.layer.Tile#getSource return type to ol.source.Tile
Remove unnecessary type cast
Don't expose olx.layer.LayerOptions