This allows the customization of the performance report.
Users can specify their own custom sequence of views.
Each view contributes a portion of the performance report generated by the
BackendPrinter.
Internally, class BackendPrinter keeps a sequence of views; views are printed
out in sequence when method 'printReport()' is called.
This patch addresses one of the two review comments from Clement in D43951.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@327018 91177308-0d34-0410-b5e6-96231b3b80d8