[clang-format] Add a test for associative map proto buffer fields
[clang-format] Add a test for associative map proto buffer fields

Summary:
The test suite was missing a test about associative maps:
https://developers.google.com/protocol-buffers/docs/proto3#maps

Reviewers: djasper

Reviewed By: djasper

Subscribers: cfe-commits, klimek

Differential Revision: https://reviews.llvm.org/D34623

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@306386 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang