add getDimensionsOnCoord.

src/data/List.js

@@ -305,6 +305,13 @@ listProto.getDimensionInfo = function (dim) {
     return this._dimensionInfos[this.getDimension(dim)];
 };
 
+/**
+ * @return {Array.<string>} concrete dimension name list on coord.
+ */
+listProto.getDimensionsOnCoord = function () {
+    return this._dimensionsSummary.dataDimsOnCoord.slice();
+};
+
 /**
  * @param {string} coordDim
  * @param {number|Array} [idx=0] A coordDim may map to more than one data dim.