Backout changeset baf184596a7b for build errors on a CLOSED TREE.
Bug 779336 - Replace DOMExpandoMap with a js::HashSet; r=bholley

--HG--
extra : rebase_source : 125fbd75b5123c17cda64c9dfe7e09b36c03bb42
Bug 861399 - Update pdf.js to version 0.8.47. r=bdahl
Bug 857989 - Add Serif/Sans Serif font toggle to Reader Mode. r=lucasr
Bug 860326 - Don't update BrowserToolbar after editing a top site on about:home. r=wesj
No bug; fix typo in header comment for gfxCallbackDrawable. comment-only, DONTBUILD
Backed out 2 changesets (bug 734691) for leaks.

Backed out changeset ba88d9730af6 (bug 734691)
Backed out changeset 7d2fbf7b0372 (bug 734691)
Bug 862440 - Remove unused aboutReaderContent.html and aboutReaderContent.css. r=bnicholson