fix(ndjson): Add ability to support content type override for ndjsone…

…ncformatter

ElasticSearch 6.x no longer supports Content-Type: "application/x-ndjson; charset=UTF-8" in the
Request Header. Older versions of Firefox append the charset=UTF-8. Elastic does support
"application/json; charset=UTF-8".

THIN-13537

src/os/net/ndjsonencformatter.js

@@ -6,16 +6,23 @@ goog.require('os.net.IDataFormatter');
 /**
  * Creates an application/json payload
  * @implements {os.net.IDataFormatter}
- * @param {Array<Object>} opt_content The JSON objects to format.
+ * @param {Array<Object>} content The JSON objects to format.
  * @param {?function(string, *)=} opt_replacer The JSON object to format.
+ * @param {string=} opt_contentType The Content-Type to set.
  * @constructor
  */
-os.net.NDJsonEncFormatter = function(opt_content, opt_replacer) {
+os.net.NDJsonEncFormatter = function(content, opt_replacer, opt_contentType) {
   /**
    * @type {Array<Object>}
    * @private
    */
-  this.content_ = opt_content;
+  this.content_ = content;
+
+  /**
+   * @type {string|undefined}
+   * @private
+   */
+  this.opt_contentType_ = opt_contentType;
 };
 
 
@@ -39,7 +46,7 @@ os.net.NDJsonEncFormatter.prototype.setContent = function(content) {
  * @inheritDoc
  */
 os.net.NDJsonEncFormatter.prototype.getContentType = function() {
-  return 'application/x-ndjson';
+  return this.opt_contentType_ || 'application/x-ndjson';
 };