See src/README for the README that ships with snappy.

Mozilla does not modify the actual snappy source with the exception of the
'snappy-stubs-public.h' header. We have replaced its build system with our own.

Snappy comes from:
  http://code.google.com/p/snappy/

We are currently using revision: 56

To upgrade to a newer version:
  1. Check out the new code using subversion.
  2. Update 'snappy-stubs-public.h' in this directory with any changes that were
     made to 'snappy-stubs-public.h.in' in the new source.
  3. Copy the major/minor/patch versions from 'configure.ac' into
     'snappy-stubs-public.h'.
  4. Copy all source files from the new version into the src subdirectory. The
     following files are not needed:
       - 'autom4te.cache' subdirectory
       - 'm4' subdirectory
       - 'testdata' subdirectory
       - 'autogen.sh'
       - 'configure.ac'
       - 'Makefile.am'
  5. Update the revision stamp in this file.