Support GeoJSON as parsed object

With this change, we can programmatically create
GeoJSONFeatureCollection objects programmatically, without
reading a GeoJSON file.

src/ol/layer/vectorlayer.js

@@ -323,6 +323,10 @@ ol.layer.Vector.prototype.parseFeatures = function(data, parser, projection) {
     goog.asserts.assert(typeof parser.readFeaturesFromString === 'function',
         'Expected a parser with readFeaturesFromString method.');
     features = parser.readFeaturesFromString(data, {callback: callback});
+  } else if (typeof data === 'object') {
+    goog.asserts.assert(typeof parser.readFeaturesFromObject === 'function',
+        'Expected a parser with a readFeaturesFromObject method.');
+    features = parser.readFeaturesFromObject(data, {callback: callback});
   } else {
     // TODO: parse more data types
     throw new Error('Data type not supported: ' + data);

src/ol/parser/geojson.js

@@ -51,6 +51,19 @@ ol.parser.GeoJSON.prototype.readFeaturesFromString =
 };
 
 
+/**
+ * Parse a GeoJSON feature collection from decoded JSON.
+ * @param {GeoJSONFeatureCollection} object GeoJSON feature collection decoded
+ *     from JSON.
+ * @param {ol.parser.ReadFeaturesOptions=} opt_options Reader options.
+ * @return {Array.<ol.Feature>} Array of features.
+ */
+ol.parser.GeoJSON.prototype.readFeaturesFromObject =
+    function(object, opt_options) {
+  return this.parseFeatureCollection_(object, opt_options);
+};
+
+
 /**
  * @param {GeoJSONObject} json GeoJSON object.
  * @return {ol.Feature|Array.<ol.Feature>|