Bug 25923 - Clarify wording in MediaKeysRequirement value descriptions.
Make the source formatting in the Security and Privacy sections consistent with the rest of the document.
Bug 27166 - Integrate more/updated text from the User Tracking (Privacy) sections of other specifications.

Some of these changes are based on review of:
* Indexed Database API: W3C Proposed Recommendation 20 November 2014 (http://www.w3.org/TR/2014/PR-IndexedDB-20141120/)
* Web Storage: Editor's Draft 14 May 2014 (http://dev.w3.org/html5/webstorage/)
Replace "domain" with "origin" in the Privacy Tracking section.