Add pixelRatio to ol.TileUrlFunction
Add pixelRatio to ol.source.Tile#getTile
Add ol.source.Tile#getTileGridForProjection
Use ol.source.Tile#getTileGridForProjection
Add ol.source.Tile#getTilePixelSize
Add HiDPI support to ol.renderer.canvas.TileLayer
Add HiDPI support to ol.renderer.webgl.TileLayer
Add HiDPI support to ol.renderer.dom.TileLayer
Add HiDPI support to ol.source.TileWMS
Activate HiDPI support in wms-tiled example
Activate HiDPI support in wms-custom-proj example
Scale WebGL output canvas by devicePixelRatio
Merge pull request #1533 from twpayne/vector-api-tile-hidpi

[vector-api] HiDPI support for tile layers