Fix playback when IE11 modifies the XML DOM (#611)

When there is a hypen contained inside manifest Location/BaseUri element and the application uses MutationObserver, IE11 can change the XML DOM of the manifest and break playback.

This changes the way the document is parsed so that it is resilient to these unintended changes.

Related IE bug: https://connect.microsoft.com/IE/feedback/details/1398926/ie11-does-not-parse-cdata-containing-hyphens-correctly

Closes #608

Author: Ross-cz

AUTHORS

@@ -29,6 +29,7 @@ Oskar Arvidsson <oskar@irock.se>
 Philo Inc. <*@philo.com>
 Robert Colantuoni <rgc@colantuoni.com>
 Roi Lipman <roilipman@gmail.com>
+Rostislav Hejduk <Ross-cz@users.noreply.github.com>
 SameGoal Inc. <*@samegoal.com>
 Sanborn Hilland <sanbornh@rogers.com>
 TalkTalk Plc <*@talktalkplc.com>

CONTRIBUTORS

@@ -43,6 +43,7 @@ Oskar Arvidsson <oskar@irock.se>
 Robert Colantuoni <rgc@colantuoni.com>
 Rohit Makasana <rohitbm@google.com>
 Roi Lipman <roilipman@gmail.com>
+Rostislav Hejduk <Ross-cz@users.noreply.github.com>
 Sam Dutton <dutton@google.com>
 Sanborn Hilland <sanbornh@rogers.com>
 Seth Madison <seth@philo.com>

lib/util/xml_utils.js

@@ -66,10 +66,13 @@ shaka.util.XmlUtils.findChildren = function(elem, name) {
  */
 shaka.util.XmlUtils.getContents = function(elem) {
   var contents = elem.firstChild;
+
+  // check content
   if (!contents || contents.nodeType != Node.TEXT_NODE)
     return null;
 
-  return contents.nodeValue.trim();
+  // read merged text content from all text nodes (fixes MSIE 11 bug)
+  return elem.textContent.trim();
 };