Their values are not used neither by the tick processor nor by CpuProfiler so it is just a waste of space.

TickSample used to be a transport for grabbed register values to TickSample::Trace, now they are passed in a special structure RegisterState which is allocated on the stack for the sampling period.

Some common pieces were moved from platform-dependent code into Sampler::SampleStack and TickSample::Init.

BUG=None
R=jkummerow@chromium.org, loislo@chromium.org

Review URL: https://codereview.chromium.org/18620002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15484 ce2b1a6d-e550-0410-aec6-3dcde31c8c00