Add pixelRatio param to ol.Image constructor

src/ol/source/imagesource.js

@@ -89,7 +89,7 @@ ol.source.Image.prototype.createImage =
   var imageUrl = this.imageUrlFunction(extent, size, projection);
   if (goog.isDef(imageUrl)) {
     image = new ol.Image(
-        extent, resolution, imageUrl, this.crossOrigin_,
+        extent, resolution, pixelRatio, imageUrl, this.crossOrigin_,
         this.getAttributions());
   }
   return image;

src/ol/source/imagewmssource.js

@@ -75,6 +75,7 @@ ol.source.ImageWMS.prototype.getImage =
   var image = this.image_;
   if (!goog.isNull(image) &&
       image.getResolution() == resolution &&
+      image.getPixelRatio() == pixelRatio &&
       ol.extent.containsExtent(image.getExtent(), extent)) {
     return image;
   }

src/ol/source/mapguidesource.js

@@ -78,6 +78,7 @@ ol.source.MapGuide.prototype.getImage =
   var image = this.image_;
   if (!goog.isNull(image) &&
       image.getResolution() == resolution &&
+      image.getPixelRatio() == pixelRatio &&
       ol.extent.containsExtent(image.getExtent(), extent)) {
     return image;
   }