Use objects instead of arrays for geometry type cache

Also trying to reference features directly here instead of
storing feature ids in the index. We'll see if this is good when
we have an index for tile coords as well and want to filter
with multiple filters, accessing multiple indices.

src/ol/source/vectorsource.js

@@ -21,7 +21,7 @@ ol.source.FeatureCache = function() {
 
 
   /**
-   * @type {Object.<string, Array.<string>>}
+   * @type {Object.<ol.Feature>}
    * @private
    */
   this.geometryTypeIndex_;
@@ -37,11 +37,11 @@ ol.source.FeatureCache = function() {
 ol.source.FeatureCache.prototype.clear = function() {
   this.idLookup_ = {};
 
-  var geometryTypeIndex_ = {};
+  var geometryTypeIndex = {};
   for (var key in ol.geom.GeometryType) {
-    geometryTypeIndex_[ol.geom.GeometryType[key]] = [];
+    geometryTypeIndex[ol.geom.GeometryType[key]] = {};
   }
-  this.geometryTypeIndex_ = geometryTypeIndex_;
+  this.geometryTypeIndex_ = geometryTypeIndex;
 };
 
 
@@ -57,7 +57,7 @@ ol.source.FeatureCache.prototype.add = function(feature) {
 
   // index by geometry type
   if (!goog.isNull(geometry)) {
-    this.geometryTypeIndex_[geometry.getType()].push(id);
+    this.geometryTypeIndex_[geometry.getType()][id] = feature;
   }
 
   /**
@@ -99,10 +99,7 @@ ol.source.FeatureCache.prototype.getFeatures = function(opt_filter) {
  * @private
  */
 ol.source.FeatureCache.prototype.getFeaturesByGeometryType_ = function(filter) {
-  var type = filter.getType(),
-      ids = this.geometryTypeIndex_[filter.getType()];
-
-  return this.getFeaturesByIds_(ids);
+  return goog.object.getValues(this.geometryTypeIndex_[filter.getType()]);
 };