[llvm-cov] Refactor "export" command implementation and add support for SOURCES.

Summary: Define an interface for Exporter + split JSON exporter into .h and .cpp.

Reviewers: vsk, morehouse

Reviewed By: vsk

Subscribers: llvm-commits, Dor1s, kcc

Differential Revision: https://reviews.llvm.org/D41600

llvm-svn: 321815
diff --git a/llvm/tools/llvm-cov/CoverageReport.h b/llvm/tools/llvm-cov/CoverageReport.h
index 1c9e68e..94611bd 100644
--- a/llvm/tools/llvm-cov/CoverageReport.h
+++ b/llvm/tools/llvm-cov/CoverageReport.h
@@ -1,4 +1,4 @@
-//===- CoverageReport.h - Code coverage report ---------------------------===//
+//===- CoverageReport.h - Code coverage report ----------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //