Add 3rd party license to each file.

LICENSE

@@ -209,7 +209,7 @@
 Apache ECharts Subcomponents:
 
 The Apache ECharts project contains subcomponents with separate copyright
-notices and license terms. Your use of the source code for the these
+notices and license terms. Your use of the source code for these
 subcomponents is subject to the terms and conditions of the following
 licenses.
 

src/chart/graph/forceHelper.js

@@ -17,6 +17,13 @@
 * under the License.
 */
 
+/*
+* The layout implementation references to d3.js. The use of
+* the source code of this file is also subject to the terms
+* and consitions of its license (BSD-3Clause, see
+* <echarts/src/licenses/LICENSE-d3>).
+*/
+
 import * as vec2 from 'zrender/src/core/vector';
 
 var scaleAndAdd = vec2.scaleAndAdd;

src/chart/tree/layoutHelper.js

@@ -17,6 +17,13 @@
 * under the License.
 */
 
+/*
+* The tree layout implementation references to d3.js
+* (https://github.com/d3/d3-hierarchy). The use of the source
+* code of this file is also subject to the terms and consitions
+* of its license (BSD-3Clause, see <echarts/src/licenses/LICENSE-d3>).
+*/
+
 /**
  * @file The layout algorithm of node-link tree diagrams. Here we using Reingold-Tilford algorithm to drawing
  *       the tree.

src/chart/treemap/treemapLayout.js

@@ -17,6 +17,14 @@
 * under the License.
 */
 
+/*
+* The treemap layout implementation references to the treemap
+* layout of d3.js (d3/src/layout/treemap.js in v3). The use of
+* the source code of this file is also subject to the terms
+* and consitions of its license (BSD-3Clause, see
+* <echarts/src/licenses/LICENSE-d3>).
+*/
+
 import * as zrUtil from 'zrender/src/core/util';
 import BoundingRect from 'zrender/src/core/BoundingRect';
 import {parsePercent, MAX_SAFE_INTEGER} from '../../util/number';
@@ -144,7 +152,8 @@ export default {
 /**
  * Layout treemap with squarify algorithm.
  * @see https://graphics.ethz.ch/teaching/scivis_common/Literature/squarifiedTreeMaps.pdf
- * @see https://github.com/mbostock/d3/blob/master/src/layout/treemap.js
+ * The implementation references to the treemap layout of d3.js.
+ * See the license statement at the head of this file.
  *
  * @protected
  * @param {module:echarts/data/Tree~TreeNode} node

src/scale/Time.js

@@ -17,6 +17,12 @@
 * under the License.
 */
 
+/*
+* The `scaleLevels` references to d3.js. The use of the source
+* code of this file is also subject to the terms and consitions
+* of its license (BSD-3Clause, see <echarts/src/licenses/LICENSE-d3>).
+*/
+
 // [About UTC and local time zone]:
 // In most cases, `number.parseDate` will treat input data string as local time
 // (except time zone is specified in time string). And `format.formateTime` returns
@@ -165,7 +171,7 @@ zrUtil.each(['contain', 'normalize'], function (methodName) {
     };
 });
 
-// Steps from d3
+// Steps from d3, see the license statement at the top of this file.
 var scaleLevels = [
     // Format              interval
     ['hh:mm:ss', ONE_SECOND],          // 1s

src/util/array/nest.js

@@ -17,6 +17,13 @@
 * under the License.
 */
 
+/*
+* The implementation references to d3.js. The use of the source
+* code of this file is also subject to the terms and consitions
+* of its license (BSD-3Clause, see <echarts/src/licenses/LICENSE-d3>).
+*/
+
+
 import * as zrUtil from 'zrender/src/core/util';
 
 /**