[llvm-cov] Make some summary info fields private. NFC.

There's a bug in the way the line and region summary objects are merged.
It would have been less likely to occur if those objects kept some data
private.

llvm-svn: 313416
diff --git a/llvm/tools/llvm-cov/CoverageSummaryInfo.cpp b/llvm/tools/llvm-cov/CoverageSummaryInfo.cpp
index d025aa8..ec263c8 100644
--- a/llvm/tools/llvm-cov/CoverageSummaryInfo.cpp
+++ b/llvm/tools/llvm-cov/CoverageSummaryInfo.cpp
@@ -87,10 +87,8 @@
   Summary.RegionCoverage = Summaries[0].RegionCoverage;
   Summary.LineCoverage = Summaries[0].LineCoverage;
   for (const auto &FCS : Summaries.drop_front()) {
-    Summary.RegionCoverage.Covered =
-        std::max(FCS.RegionCoverage.Covered, Summary.RegionCoverage.Covered);
-    Summary.LineCoverage.Covered =
-        std::max(FCS.LineCoverage.Covered, Summary.LineCoverage.Covered);
+    Summary.RegionCoverage.merge(FCS.RegionCoverage);
+    Summary.LineCoverage.merge(FCS.LineCoverage);
   }
   return Summary;
 }