Refactor some code in SampleProfile.cpp

Refactor some code in SampleProfile.cpp

I'm adding new functionality in the sample profiler. This will
require more data to be kept around for each function, so I moved
the structure SampleProfile that we keep for each function into
a separate class.

There are no functional changes in this patch. It simply provides
a new home where to place all the new data that I need to propagate
weights through edges.

There are some other name and minor edits throughout.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195780 91177308-0d34-0410-b5e6-96231b3b80d8