Add support for multiple tileSizes in the tilegrid.

This is needed by WMTS.

src/ol/renderer/canvas/canvastilelayerrenderer.js

@@ -91,8 +91,8 @@ ol.renderer.canvas.TileLayer.prototype.renderFrame =
   var tileSource = tileLayer.getTileSource();
   var tileSourceKey = goog.getUid(tileSource).toString();
   var tileGrid = tileSource.getTileGrid();
-  var tileSize = tileGrid.getTileSize();
   var z = tileGrid.getZForResolution(view2DState.resolution);
+  var tileSize = tileGrid.getTileSize(z);
   var tileResolution = tileGrid.getResolution(z);
   var tileRange = tileGrid.getTileRangeForExtentAndResolution(
       frameState.extent, tileResolution);

src/ol/renderer/dom/domtilelayerrenderer.js

@@ -292,7 +292,7 @@ ol.renderer.dom.TileLayerZ_.prototype.addTile = function(tile) {
   if (tileCoordKey in this.tiles_) {
     return;
   }
-  var tileSize = this.tileGrid_.getTileSize();
+  var tileSize = this.tileGrid_.getTileSize(tileCoord.z);
   var image = tile.getImage(this);
   var style = image.style;
   style.position = 'absolute';

src/ol/renderer/webgl/webgltilelayerrenderer.js

@@ -299,7 +299,7 @@ ol.renderer.webgl.TileLayer.prototype.renderFrame =
   } else {
 
     var tileRangeSize = tileRange.getSize();
-    var tileSize = tileGrid.getTileSize();
+    var tileSize = tileGrid.getTileSize(z);
 
     var maxDimension = Math.max(
         tileRangeSize.width * tileSize.width,