Check in code change for implementing Performace Schema in InnoDB.
Objects in four different modules in InnoDB have been performance
instrumented, these modules are:
1) mutexes
2) rwlocks
3) file I/O
4) threads

We mostly preserved the existing APIs, but APIs would point to
instrumented function wrappers if performance schema is defined.
There are 4 different defines that controls the instrumentation of
each module.  The feature is off by default, and will be compiled in
with special build option, and requre configure option to turn it on
when server boots.  For more detail design and functional information,
please refer to performance schema wiki page.

rb://270 approved by Marko Mäkelä