First pass at logging infrastructure.  Not finished yet.
No bug - Fix typo in comment in mfbt/HashFunctions.h.  DONTBUILD
Now logging sort of works.
Bug XXX - Don't -Ixpcom/base in media/webrt/signaling.

We try to namespace Mozilla headers by exporting them into the mozilla/ directory.  But -Ixpcom/base breaks this namespacing.  Webrtc includes "logging.h", which conflicts with xpcom/base/Logging.h on case-insensitive FS's.  xpcom/base/Logging.h should be included as "mozilla/Logging.h", so we shouldn't have this problem if we don't abuse -I.
LOG_AS_STR works!
Got rid of prlog in nsDocShell.cpp.
Switched nsDocument and nsSHistory over to the new logging, but I need to add cross-cutting logging for CSP.
Adding log modules.
Improving PRINT logic in Logging.cpp.
Switching ProcessPriorityManager to mozilla/Logging.h.
INCOMPLETE: Change IPC logging to mozilla/Logging.h.