MDL-34674 use browser built-in spell checking in all browsers except < IE10

lib/editor/tinymce/plugins/spellchecker/lang/en/tinymce_spellchecker.php

@@ -22,6 +22,6 @@
  * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
-$string['pluginname'] = 'Check spelling';
+$string['pluginname'] = 'Legacy spell checker';
 
 /* This plugin abuses strings from the standard TinyMCE spellchecker plugin, there is no need to duplicate them here. */

lib/editor/tinymce/plugins/spellchecker/lib.php

@@ -32,6 +32,10 @@ class tinymce_spellchecker extends editor_tinymce_plugin {
             array $options = null) {
         global $CFG;
 
+        if (!$this->is_legacy_browser()) {
+            return;
+        }
+
         // Check at least one language is supported.
         $spelllanguagelist = $this->get_config('spelllanguagelist', '');
         if ($spelllanguagelist !== '') {
@@ -48,4 +52,13 @@ class tinymce_spellchecker extends editor_tinymce_plugin {
             $params['spellchecker_languages'] = $spelllanguagelist;
         }
     }
+
+    protected function is_legacy_browser() {
+        // IE8 and IE9 are the only supported browsers that do not have spellchecker.
+        if (check_browser_version('MSIE', 5) and !check_browser_version('MSIE', 10)) {
+            return true;
+        }
+        // The rest of browsers supports spellchecking or is horribly outdated and we do not care...
+        return false;
+    }
 }