Bug 847521 - Allow CheckedInt<signed char> in addition to char/unsigned char.  char != signed char (but is guaranteed to have the same representation as either signed char or unsigned char, for backwards-compatibility reasons), so we have to handle signed char as a third character type.  r=bjacob

--HG--
rename : content/html/content/src/HTMLObjectElement.h => content/html/content/src/HTMLObjectElement.cpp
extra : rebase_source : d07d72b78fcbae31483d726703b3605561295684
Bug 842715: Refactor gUM prefs use to be on mainthread, and prepare for constraints r=derf