Bug 1042876 - Update newtab endpoints to new v2/links [r=adw]

Point to new endpoints that can be strict on types, so request the appropriate content type.

browser/app/profile/firefox.js

@@ -1531,7 +1531,7 @@ pref("browser.newtabpage.rows", 3);
 pref("browser.newtabpage.columns", 5);
 
 // directory tiles download URL
-pref("browser.newtabpage.directory.source", "chrome://global/content/directoryLinks.json");
+pref("browser.newtabpage.directory.source", "https://tiles.up.mozillalabs.com/v2/links/fetch");
 
 // endpoint to send newtab click and view pings
 pref("browser.newtabpage.directory.ping", "https://tiles.up.mozillalabs.com/v2/links/");

toolkit/content/jar.mn

@@ -37,9 +37,6 @@ toolkit.jar:
 *  content/global/customizeToolbar.js         (customizeToolbar.js)
    content/global/customizeToolbar.xul        (customizeToolbar.xul)
    content/global/devicestorage.properties    (devicestorage.properties)
-#ifndef ANDROID
-   content/global/directoryLinks.json         (directoryLinks.json)
-#endif
    content/global/editMenuOverlay.js          (editMenuOverlay.js)
 *+ content/global/editMenuOverlay.xul         (editMenuOverlay.xul)
    content/global/finddialog.js               (finddialog.js)

toolkit/modules/DirectoryLinksProvider.jsm

@@ -28,6 +28,7 @@ XPCOMUtils.defineLazyGetter(this, "gTextDecoder", () => {
 
 // The filename where directory links are stored locally
 const DIRECTORY_LINKS_FILE = "directoryLinks.json";
+const DIRECTORY_LINKS_TYPE = "application/json";
 
 // The preference that tells whether to match the OS locale
 const PREF_MATCH_OS_LOCALE = "intl.locale.matchOS";
@@ -194,7 +195,6 @@ let DirectoryLinksProvider = {
   _fetchAndCacheLinks: function DirectoryLinksProvider_fetchAndCacheLinks(uri) {
     let deferred = Promise.defer();
     let xmlHttp = new XMLHttpRequest();
-    xmlHttp.overrideMimeType("application/json");
 
     let self = this;
     xmlHttp.onload = function(aResponse) {
@@ -217,6 +217,10 @@ let DirectoryLinksProvider = {
 
     try {
       xmlHttp.open('POST', uri);
+      // Override the type so XHR doesn't complain about not well-formed XML
+      xmlHttp.overrideMimeType(DIRECTORY_LINKS_TYPE);
+      // Set the appropriate request type for servers that require correct types
+      xmlHttp.setRequestHeader("Content-Type", DIRECTORY_LINKS_TYPE);
       xmlHttp.send(JSON.stringify({
         locale: this.locale,
       }));