add allowfullscreen tags to the rce

test plan:
- add add a video in an iframe in the rich content editor
- it should be able to become full screen

fixes PLAT-647

Change-Id: I05ad81fdebc32353af9746605e9847947e614582
Reviewed-on: https://gerrit.instructure.com/41728
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Nathan Mills <nathanm@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Product-Review: Brad Humphrey <brad@instructure.com>

gems/canvas_sanitize/lib/canvas_sanitize/canvas_sanitize.rb

@@ -130,7 +130,7 @@ module CanvasSanitize #:nodoc:
           'col' => ['span', 'width'],
           'colgroup' => ['span', 'width'],
           'img' => ['align', 'alt', 'height', 'src', 'width'],
-          'iframe' => ['src', 'width', 'height', 'name', 'align', 'frameborder', 'scrolling', 'sandbox', 'allowfullscreen'],
+          'iframe' => ['src', 'width', 'height', 'name', 'align', 'frameborder', 'scrolling', 'sandbox', 'allowfullscreen','webkitallowfullscreen','mozallowfullscreen'],
           'ol' => ['start', 'type'],
           'q' => ['cite'],
           'table' => ['summary', 'width', 'border', 'cellpadding', 'cellspacing', 'center', 'frame', 'rules', 'dir', 'lang'],

public/javascripts/tinymce.editor_box.js

@@ -166,7 +166,7 @@ define([
       theme_advanced_resizing : true,
       theme_advanced_blockformats : "p,h2,h3,h4,pre",
       theme_advanced_more_colors: false,
-      extended_valid_elements : "iframe[src|width|height|name|align|style|class|sandbox]",
+      extended_valid_elements : "iframe[src|width|height|name|align|style|class|sandbox|allowfullscreen|webkitallowfullscreen|mozallowfullscreen]",
       content_css: "/stylesheets_compiled/legacy_normal_contrast/vendor/instructure_style.css,/stylesheets_compiled/legacy_normal_contrast/vendor/tinymce.editor_box.css",
       editor_css: editor_css,
       auto_focus: options.focus ? id : null,

public/javascripts/tinymce/jscripts/tiny_mce/plugins/instructure_external_tools/editor_plugin.js

@@ -114,7 +114,10 @@ define([
               } else if(data.return_type == 'iframe') {
                 var html = $("<div/>").append($("<iframe/>", {
                   src: data.url,
-                  title: data.title
+                  title: data.title,
+                  allowfullscreen: "true",
+                  webkitallowfullscreen: "true",
+                  mozallowfullscreen: "true"
                 }).css({
                   width: data.width,
                   height: data.height