Interface for GetFeatureInfo

When a source implements this interface, the layer renderer can
access the source to get feature info.

src/ol/source/featureinfosource.js

@@ -0,0 +1,18 @@
+goog.provide('ol.source.FeatureInfoSource');
+
+
+
+/**
+ * @interface
+ */
+ol.source.FeatureInfoSource = function() {};
+
+
+/**
+ * @param {ol.Pixel} pixel Pixel.
+ * @param {ol.Map} map The map that the pixel belongs to.
+ * @param {function(string)} success Callback with feature info.
+ * @param {function()=} opt_error Optional error callback.
+ */
+ol.source.FeatureInfoSource.prototype.getFeatureInfoForPixel =
+    goog.abstractMethod;