Bug 1349437 - Add "save as" support for JSON Viewer. r=honza

Based on https://github.com/mozilla/pdf.js/commit/04599bc4

--HG--
extra : rebase_source : 4902f963895601d40763fc2145f37c7ff7c5bcbc

devtools/client/jsonview/converter-child.js

@@ -96,6 +96,10 @@ Converter.prototype = {
     this.charset =
       request.QueryInterface(Ci.nsIChannel).contentCharset || "UTF-8";
 
+    // Let "save as" save the original JSON, not the viewer
+    request.QueryInterface(Ci.nsIWritablePropertyBag);
+    request.setProperty("contentType", "application/json");
+
     this.channel = request;
     this.channel.contentType = "text/html";
     this.channel.contentCharset = "UTF-8";