Replace source ready flag with loading/ready/error enum

src/ol/layer/layer.js

@@ -68,17 +68,17 @@ ol.layer.Layer.prototype.getSource = function() {
 };
 
 
+/**
+  * @inheritDoc
+  */
+ol.layer.Layer.prototype.getSourceState = function() {
+  return this.getSource().getState();
+};
+
+
 /**
  * @private
  */
 ol.layer.Layer.prototype.handleSourceChange_ = function() {
   this.dispatchChangeEvent();
 };
-
-
-/**
- * @inheritDoc
- */
-ol.layer.Layer.prototype.isReady = function() {
-  return this.getSource().isReady();
-};