[llvm-cov] Add an option for "export" command to emit only file summary data.

Summary:
That allows to get the same data as produced by "llvm-cov report",
but in JSON format, which is better for further processing by end users.

Reviewers: vsk

Reviewed By: vsk

Differential Revision: https://reviews.llvm.org/D41085

llvm-svn: 320435
diff --git a/llvm/tools/llvm-cov/CodeCoverage.cpp b/llvm/tools/llvm-cov/CodeCoverage.cpp
index 2ecd7ea..00258f2 100644
--- a/llvm/tools/llvm-cov/CodeCoverage.cpp
+++ b/llvm/tools/llvm-cov/CodeCoverage.cpp
@@ -631,6 +631,10 @@
       "show-instantiation-summary", cl::Optional,
       cl::desc("Show instantiation statistics in summary table"));
 
+  cl::opt<bool> SummaryOnly(
+      "summary-only", cl::Optional,
+      cl::desc("Export only summary information for each source file"));
+
   auto commandLineParser = [&, this](int argc, const char **argv) -> int {
     cl::ParseCommandLineOptions(argc, argv, "LLVM code coverage tool\n");
     ViewOpts.Debug = DebugDump;
@@ -743,6 +747,7 @@
 
     ViewOpts.ShowRegionSummary = RegionSummary;
     ViewOpts.ShowInstantiationSummary = InstantiationSummary;
+    ViewOpts.ExportSummaryOnly = SummaryOnly;
 
     return 0;
   };