Bug 919889 (part 1) - Rename jsmemorymetrics.cpp as vm/MemoryMetrics.cpp.  r=luke.

--HG--
rename : js/src/jsmemorymetrics.cpp => js/src/vm/MemoryMetrics.cpp
Bug 919889 (part 2) - Rename IteratorClosure as StatsClosure.  r=luke.
Bug 919889 (part 3) - Move the private_ field out of ObjectsExtraSizes.  r=luke.
Bug 919889 (part 4) - Assorted minor clean-ups.  r=luke.
Bug 919889 (part 5) - Use macros to eliminate repetitive, error-prone code in MemoryMetrics.{h,cpp}.  r=luke.