This is done by adding a USE_BOOST compile time flag that is enabled by default
when the library is compiled with CMake (mainly for external users).
In Chromium, the library will be built without the USE_BOOST compile time flag.
Instead the NO_THREAD_SAFETY flag will have to be provided so that the minimal
non-thread-safe subset of base will be used.
This is possible since libphonenumber is only used from the UI thread in
Chromium.
BUG=http://crbug.com/236272R=jia.shao.peng@gmail.com
Review URL: https://codereview.appspot.com/8859052
Gilles Vollant
dvadym
Nico Weber
Philippe Liard