Back in 02/08 when we added android_atomic_inc/dec, for

Back in 02/08 when we added android_atomic_inc/dec, for
some reason, it missed define WTF_USE_LOCKFREE_THREADSAFESHARED.
So we are using mutexlocker instead of refcount inc/dec.
Even mutex version should work, but it is not exercised
by win/darwin/gcc. Changing to use refcount version fixed
the crash seen in picasaweb.

Fix http://b/issue?id=2183371
Maybe fix http://b/issue?id=2165237. But I can't verify
as I can't reproduce it even before my change.