Write modifications back to the original layer

With the feature's getOriginal() and setOriginal() methods, an
undo tree can be maintained now.

src/ol/feature.js

@@ -42,6 +42,13 @@ ol.Feature = function(opt_values) {
    */
   this.geometryName_;
 
+  /**
+   * Original of this feature when it was modified.
+   * @type {ol.Feature}
+   * @private
+   */
+  this.original_ = null;
+
   /**
    * The render intent for this feature.
    * @type {ol.layer.VectorLayerRenderIntent|string}
@@ -101,6 +108,15 @@ ol.Feature.prototype.getGeometry = function() {
 };
 
 
+/**
+ * Get the original of this feature when it was modified.
+ * @return {ol.Feature} Original.
+ */
+ol.Feature.prototype.getOriginal = function() {
+  return this.original_;
+};
+
+
 /**
  * Get any symbolizers set directly on the feature.
  * @return {Array.<ol.style.Symbolizer>} Symbolizers (or null if none).
@@ -176,6 +192,15 @@ ol.Feature.prototype.setGeometry = function(geometry) {
 };
 
 
+/**
+ * Set the original of this feature when it was modified.
+ * @param {ol.Feature} original Original.
+ */
+ol.Feature.prototype.setOriginal = function(original) {
+  this.original_ = original;
+};
+
+
 /**
  * Gets the renderIntent for this feature.
  * @return {string} Render intent.

src/ol/interaction/modifyinteraction.js

@@ -172,7 +172,8 @@ ol.interaction.Modify.prototype.addSegments_ =
 ol.interaction.Modify.prototype.handleDragStart = function(evt) {
   this.dragSegments_ = [];
   for (var i = 0, ii = this.layers_.length; i < ii; ++i) {
-    var selectionData = this.layers_[i].getSelectionData();
+    var layer = this.layers_[i];
+    var selectionData = layer.getSelectionData();
     var selectionLayer = selectionData.layer;
     if (!goog.isNull(selectionLayer)) {
       var editData = selectionLayer.getEditData();
@@ -186,16 +187,22 @@ ol.interaction.Modify.prototype.handleDragStart = function(evt) {
         for (var j = 0, jj = segments.length; j < jj; ++j) {
           var segmentData = segments[j];
           var segment = segmentData[0];
+          var feature = segmentData[1];
+          var featureId = goog.getUid(feature);
+          var original = selectionData.featuresBySelectedFeatureUid[featureId];
           if (vertexFeature.renderIntent ==
               ol.layer.VectorLayerRenderIntent.TEMPORARY) {
             if (ol.coordinate.equals(segment[0], vertex)) {
               this.dragSegments_.push([selectionLayer, segmentData, 0]);
-            } else {
+              feature.setOriginal(original);
+            } else if (ol.coordinate.equals(segment[1], vertex)) {
               this.dragSegments_.push([selectionLayer, segmentData, 1]);
+              feature.setOriginal(original);
             }
           } else if (
               ol.coordinate.squaredDistanceToSegment(vertex, segment) === 0) {
             insertVertices.push([selectionLayer, segmentData, vertex]);
+            feature.setOriginal(original);
           }
         }
         for (j = insertVertices.length - 1; j >= 0; --j) {