Pulled out cast detection in TokenAnnotator into its own function
This is to remove FIXME added in r207964.

Differential Revision: http://reviews.llvm.org/D3619



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@208071 91177308-0d34-0410-b5e6-96231b3b80d8