[Tooling] [1/1] Refactor FrontendActionFactory::create() to return std::unique_ptr<>
Summary:
I'm not sure whether there are any principal reasons why it returns raw owning pointer,
or it is just a old code that was not updated post-C++11.
I'm not too sure what testing i should do, because `check-all` is not error clean here for some reason,
but it does not //appear// asif those failures are related to these changes.
This is Clang-tools-extra part.
Clang part is D43779.
Reviewers: klimek, bkramer, alexfh, pcc
Reviewed By: alexfh
Subscribers: ioeric, jkorous-apple, cfe-commits
Tags: #clang, #clang-tools-extra
Differential Revision: https://reviews.llvm.org/D43780
llvm-svn: 326202