[analyzer][NFC] Refactoring BugReporter.cpp P3.: std::shared_pointer<PathDiagnosticPi...

[analyzer][NFC] Refactoring BugReporter.cpp P3.: std::shared_pointer<PathDiagnosticPiece> -> PathDiagnosticPieceRef

find clang/ -type f -exec sed -i 's/std::shared_ptr<PathDiagnosticPiece>/PathDiagnosticPieceRef/g' {} \;
git diff -U3 --no-color HEAD^ | clang-format-diff-6.0 -p1 -i

Just as C++ is meant to be refactored, right?

Differential Revision: https://reviews.llvm.org/D65381

llvm-svn: 368717