Add support for profiling the matchers used.

Summary:
Add support for profiling the matchers used.
This will be connected with clang-tidy to generate a report to determine
and debug slow checks.

Reviewers: alexfh

Subscribers: klimek, cfe-commits

Differential Revision: http://reviews.llvm.org/D5911

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@220418 91177308-0d34-0410-b5e6-96231b3b80d8