AU: Common code to parse simple key/value store files

AU: Common code to parse simple key/value store files

We use a few files, like /etc/lsb-release, that have a simple
key/value store format: each line is a key/value pair and the
key/value are separated by '='. This change make some common code to
parse (and assemble) these files, which is used in one place now but
will be used in another place soon, too.

BUG=None
TEST=attached unittests

[davidjames, 2010-05-21 21:40:53]

LGTM w/nit

http://codereview.chromium.org/2105016/diff/1/4
File src/platform/update_engine/simple_key_value_store.cc (right):

http://codereview.chromium.org/2105016/diff/1/4#newcode29
src/platform/update_engine/simple_key_value_store.cc:29: ret[it->substr(0, pos)]
= it->substr(pos + 1, it->size());
Do you mean just it->substr(pos + 1)?