Add the capability to remove(undo) the last drawed segments.

src/ol/interaction/drawinteraction.js

@@ -617,6 +617,31 @@ ol.interaction.Draw.prototype.addToDrawing_ = function(event) {
 };
 
 
+/**
+ * Remove last drawed point of the currently edited feature.
+ * @api
+ */
+ol.interaction.Draw.prototype.removeLastPoint = function() {
+  var geometry = this.sketchFeature_.getGeometry();
+  var coordinates, sketchLineGeom;
+  if (this.mode_ === ol.interaction.DrawMode.LINE_STRING) {
+    coordinates = this.sketchCoords_;
+    coordinates.splice(-2, 1);
+    this.geometryFunction_(coordinates, geometry);
+  } else if (this.mode_ === ol.interaction.DrawMode.POLYGON) {
+    coordinates = this.sketchCoords_[0];
+    coordinates.splice(-2, 1);
+    sketchLineGeom = this.sketchLine_.getGeometry();
+    sketchLineGeom.setCoordinates(coordinates);
+    this.geometryFunction_(this.sketchCoords_, geometry);
+  }
+
+  if (coordinates.length === 0) this.finishCoordinate_ = null;
+
+  this.updateSketchFeatures_();
+};
+
+
 /**
  * Stop drawing and add the sketch feature to the target layer.
  * The {@link ol.interaction.DrawEventType.DRAWEND} event is dispatched before