Move *BSD and Solaris Sampler implementation into sampler.cc

This is a first step to having profiler sampler implementation in one file with platform capabilities guarded with #ifdef. Otherwise we have very similar implementations scattered over platform-*.cc files which makes it hard to see differences and make changes.

The next steps will be to merge win32, Mac OS X and Cygwin implementations into sampler.cc They suspend profiled thread instead of sending a signal but apart from that the logic is pretty much the same. Then I'm going to move sampler-related code from log.* into sampler.*

BUG=None

Review URL: https://codereview.chromium.org/13852005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14265 ce2b1a6d-e550-0410-aec6-3dcde31c8c00