Keep track of tile source count

externs/olx.js

@@ -7008,6 +7008,7 @@ olx.view.FitOptions.prototype.maxZoom;
  *     size: ol.Size,
  *     skippedFeatureUids: Object.<string, boolean>,
  *     tileQueue: ol.TileQueue,
+ *     tileSourceCount: number,
  *     time: number,
  *     usedTiles: Object.<string, Object.<string, ol.TileRange>>,
  *     viewState: olx.ViewState,

src/ol/map.js

@@ -1027,7 +1027,7 @@ ol.Map.prototype.handlePostRender = function() {
         maxTotalLoading = this.loadTilesWhileInteracting_ ? 8 : 0;
         maxNewLoads = 2;
       }
-      tileSourceCount = Object.keys(frameState.wantedTiles).length;
+      tileSourceCount = frameState.tileSourceCount;
     }
     maxTotalLoading *= tileSourceCount;
     maxNewLoads *= tileSourceCount;
@@ -1332,6 +1332,7 @@ ol.Map.prototype.renderFrame_ = function(time) {
       size: size,
       skippedFeatureUids: this.skippedFeatureUids_,
       tileQueue: this.tileQueue_,
+      tileSourceCount: 0,
       time: time,
       usedTiles: {},
       viewState: viewState,

src/ol/renderer/layerrenderer.js

@@ -298,6 +298,7 @@ ol.renderer.Layer.prototype.manageTilePyramid = function(
   var tileSourceKey = goog.getUid(tileSource).toString();
   if (!(tileSourceKey in frameState.wantedTiles)) {
     frameState.wantedTiles[tileSourceKey] = {};
+    ++frameState.tileSourceCount;
   }
   var wantedTiles = frameState.wantedTiles[tileSourceKey];
   var tileQueue = frameState.tileQueue;

src/ol/source/rastersource.js

@@ -122,6 +122,7 @@ ol.source.Raster = function(options) {
     size: [0, 0],
     skippedFeatureUids: {},
     tileQueue: this.tileQueue_,
+    tileSourceCount: 0,
     time: Date.now(),
     usedTiles: {},
     viewState: /** @type {olx.ViewState} */ ({